lo/slice_test.go

package lo

import (
	"errors"
	"fmt"
	"math"
	"sort"
	"strconv"
	"strings"
	"testing"

	"github.com/stretchr/testify/assert"
)

func TestFilter(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	r1 := Filter([]int{1, 2, 3, 4}, func(x, _ int) bool {
		return x%2 == 0
	})
	is.Equal([]int{2, 4}, r1)

	r2 := Filter([]string{"", "foo", "", "bar", ""}, func(x string, _ int) bool {
		return len(x) > 0
	})
	is.Equal([]string{"foo", "bar"}, r2)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Filter(allStrings, func(x string, _ int) bool {
		return len(x) > 0
	})
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestFilterErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	tests := []struct {
		name      string
		input     []int
		predicate func(item, index int) (bool, error)
		want      []int
		wantErr   string
		callbacks int // Number of predicates called before error/finish
	}{
		{
			name:  "filter even numbers",
			input: []int{1, 2, 3, 4},
			predicate: func(x, _ int) (bool, error) {
				return x%2 == 0, nil
			},
			want:      []int{2, 4},
			callbacks: 4,
		},
		{
			name:  "empty slice",
			input: []int{},
			predicate: func(x, _ int) (bool, error) {
				return true, nil
			},
			want:      []int{},
			callbacks: 0,
		},
		{
			name:  "filter all out",
			input: []int{1, 2, 3, 4},
			predicate: func(x, _ int) (bool, error) {
				return false, nil
			},
			want:      []int{},
			callbacks: 4,
		},
		{
			name:  "filter all in",
			input: []int{1, 2, 3, 4},
			predicate: func(x, _ int) (bool, error) {
				return true, nil
			},
			want:      []int{1, 2, 3, 4},
			callbacks: 4,
		},
		{
			name:  "error on specific index",
			input: []int{1, 2, 3, 4},
			predicate: func(x, _ int) (bool, error) {
				if x == 3 {
					return false, errors.New("number 3 is not allowed")
				}
				return x%2 == 0, nil
			},
			callbacks: 3,
			wantErr:   "number 3 is not allowed",
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			var callbacks int
			wrappedPredicate := func(item, index int) (bool, error) {
				callbacks++
				return tt.predicate(item, index)
			}

			got, err := FilterErr(tt.input, wrappedPredicate)

			if tt.wantErr != "" {
				is.Error(err)
				is.Equal(tt.wantErr, err.Error())
				is.Nil(got)
				is.Equal(tt.callbacks, callbacks, "callback count should match expected early return")
			} else {
				is.NoError(err)
				is.Equal(tt.want, got)
				is.Equal(tt.callbacks, callbacks)
			}
		})
	}

	// Test type preservation
	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty, err := FilterErr(allStrings, func(x string, _ int) (bool, error) {
		return len(x) > 0, nil
	})
	is.NoError(err)
	is.IsType(nonempty, allStrings, "type preserved")
	is.Equal(myStrings{"foo", "bar"}, nonempty)
}

func TestMap(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Map([]int{1, 2, 3, 4}, func(x, _ int) string {
		return "Hello"
	})
	result2 := Map([]int64{1, 2, 3, 4}, func(x int64, _ int) string {
		return strconv.FormatInt(x, 10)
	})

	is.Equal([]string{"Hello", "Hello", "Hello", "Hello"}, result1)
	is.Equal([]string{"1", "2", "3", "4"}, result2)
}

func TestMapErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	tests := []struct {
		name                  string
		input                 []int
		transform             func(item, index int) (string, error)
		wantResult            []string
		wantErr               bool
		errMsg                string
		expectedCallbackCount int
	}{
		{
			name:  "successful transformation",
			input: []int{1, 2, 3, 4},
			transform: func(x, _ int) (string, error) {
				return strconv.Itoa(x), nil
			},
			wantResult:            []string{"1", "2", "3", "4"},
			wantErr:               false,
			expectedCallbackCount: 4,
		},
		{
			name:  "error at third element stops iteration",
			input: []int{1, 2, 3, 4},
			transform: func(x, _ int) (string, error) {
				if x == 3 {
					return "", errors.New("number 3 is not allowed")
				}
				return strconv.Itoa(x), nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 3 is not allowed",
			expectedCallbackCount: 3,
		},
		{
			name:  "error at first element stops iteration immediately",
			input: []int{1, 2, 3, 4},
			transform: func(x, _ int) (string, error) {
				if x == 1 {
					return "", errors.New("number 1 is not allowed")
				}
				return strconv.Itoa(x), nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 1 is not allowed",
			expectedCallbackCount: 1,
		},
		{
			name:  "error at last element",
			input: []int{1, 2, 3, 4},
			transform: func(x, _ int) (string, error) {
				if x == 4 {
					return "", errors.New("number 4 is not allowed")
				}
				return strconv.Itoa(x), nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 4 is not allowed",
			expectedCallbackCount: 4,
		},
		{
			name:  "empty input slice",
			input: []int{},
			transform: func(x, _ int) (string, error) {
				return strconv.Itoa(x), nil
			},
			wantResult:            []string{},
			wantErr:               false,
			expectedCallbackCount: 0,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			// Track callback count to test early return
			callbackCount := 0
			wrappedTransform := func(item, index int) (string, error) {
				callbackCount++
				return tt.transform(item, index)
			}

			result, err := MapErr(tt.input, wrappedTransform)

			if tt.wantErr {
				is.Error(err)
				is.Equal(tt.errMsg, err.Error())
				is.Nil(result)
			} else {
				is.NoError(err)
				is.Equal(tt.wantResult, result)
			}

			// Verify callback count matches expected
			is.Equal(tt.expectedCallbackCount, callbackCount, "callback count should match expected")
		})
	}
}

func TestUniqMap(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	type User struct {
		Name string
		age  int
	}

	users := []User{{Name: "Alice", age: 20}, {Name: "Alex", age: 21}, {Name: "Alex", age: 22}}
	result := UniqMap(users, func(item User, index int) string {
		return item.Name
	})

	sort.Strings(result)

	is.Equal([]string{"Alex", "Alice"}, result)
}

func TestFilterMap(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	r1 := FilterMap([]int64{1, 2, 3, 4}, func(x int64, _ int) (string, bool) {
		if x%2 == 0 {
			return strconv.FormatInt(x, 10), true
		}
		return "", false
	})
	r2 := FilterMap([]string{"cpu", "gpu", "mouse", "keyboard"}, func(x string, _ int) (string, bool) {
		if strings.HasSuffix(x, "pu") {
			return "xpu", true
		}
		return "", false
	})

	is.Equal([]string{"2", "4"}, r1)
	is.Equal([]string{"xpu", "xpu"}, r2)
}

func TestFlatMap(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := FlatMap([]int{0, 1, 2, 3, 4}, func(x, _ int) []string {
		return []string{"Hello"}
	})
	result2 := FlatMap([]int64{0, 1, 2, 3, 4}, func(x int64, _ int) []string {
		result := make([]string, 0, x)
		for i := int64(0); i < x; i++ {
			result = append(result, strconv.FormatInt(x, 10))
		}
		return result
	})

	is.Equal([]string{"Hello", "Hello", "Hello", "Hello", "Hello"}, result1)
	is.Equal([]string{"1", "2", "2", "3", "3", "3", "4", "4", "4", "4"}, result2)
}

func TestFlatMapErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	tests := []struct {
		name                  string
		input                 []int64
		transform             func(item int64, index int) ([]string, error)
		wantResult            []string
		wantErr               bool
		errMsg                string
		expectedCallbackCount int
	}{
		{
			name:  "successful transformation",
			input: []int64{0, 1, 2},
			transform: func(x int64, _ int) ([]string, error) {
				return []string{strconv.FormatInt(x, 10), strconv.FormatInt(x, 10)}, nil
			},
			wantResult:            []string{"0", "0", "1", "1", "2", "2"},
			wantErr:               false,
			expectedCallbackCount: 3,
		},
		{
			name:  "error at second element stops iteration",
			input: []int64{0, 1, 2, 3},
			transform: func(x int64, _ int) ([]string, error) {
				if x == 1 {
					return nil, errors.New("number 1 is not allowed")
				}
				return []string{strconv.FormatInt(x, 10)}, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 1 is not allowed",
			expectedCallbackCount: 2,
		},
		{
			name:  "error at first element stops iteration immediately",
			input: []int64{0, 1, 2, 3},
			transform: func(x int64, _ int) ([]string, error) {
				if x == 0 {
					return nil, errors.New("number 0 is not allowed")
				}
				return []string{strconv.FormatInt(x, 10)}, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 0 is not allowed",
			expectedCallbackCount: 1,
		},
		{
			name:  "error at last element",
			input: []int64{0, 1, 2},
			transform: func(x int64, _ int) ([]string, error) {
				if x == 2 {
					return nil, errors.New("number 2 is not allowed")
				}
				return []string{strconv.FormatInt(x, 10)}, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 2 is not allowed",
			expectedCallbackCount: 3,
		},
		{
			name:  "empty input slice",
			input: []int64{},
			transform: func(x int64, _ int) ([]string, error) {
				return []string{strconv.FormatInt(x, 10)}, nil
			},
			wantResult:            []string{},
			wantErr:               false,
			expectedCallbackCount: 0,
		},
		{
			name:  "returns empty slice for each element",
			input: []int64{1, 2, 3},
			transform: func(x int64, _ int) ([]string, error) {
				return []string{}, nil
			},
			wantResult:            []string{},
			wantErr:               false,
			expectedCallbackCount: 3,
		},
		{
			name:  "returns nil for some elements",
			input: []int64{1, 2, 3},
			transform: func(x int64, _ int) ([]string, error) {
				if x == 2 {
					return nil, nil
				}
				return []string{strconv.FormatInt(x, 10)}, nil
			},
			wantResult:            []string{"1", "3"},
			wantErr:               false,
			expectedCallbackCount: 3,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			// Track callback count to test early return
			callbackCount := 0
			wrappedTransform := func(item int64, index int) ([]string, error) {
				callbackCount++
				return tt.transform(item, index)
			}

			result, err := FlatMapErr(tt.input, wrappedTransform)

			if tt.wantErr {
				is.Error(err)
				is.Equal(tt.errMsg, err.Error())
				is.Nil(result)
			} else {
				is.NoError(err)
				is.Equal(tt.wantResult, result)
			}

			// Verify callback count matches expected
			is.Equal(tt.expectedCallbackCount, callbackCount, "callback count should match expected")
		})
	}
}

func TestTimes(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Times(3, func(i int) string {
		return strconv.FormatInt(int64(i), 10)
	})
	is.Equal([]string{"0", "1", "2"}, result1)
}

func TestReduce(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Reduce([]int{1, 2, 3, 4}, func(agg, item, _ int) int {
		return agg + item
	}, 0)
	result2 := Reduce([]int{1, 2, 3, 4}, func(agg, item, _ int) int {
		return agg + item
	}, 10)

	is.Equal(10, result1)
	is.Equal(20, result2)
}

func TestReduceErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	tests := []struct {
		name                  string
		input                 []int
		accumulator           func(agg, item, index int) (int, error)
		initial               int
		wantResult            int
		wantErr               bool
		errMsg                string
		expectedCallbackCount int
	}{
		{
			name:  "successful reduction",
			input: []int{1, 2, 3, 4},
			accumulator: func(agg, item, _ int) (int, error) {
				return agg + item, nil
			},
			initial:               0,
			wantResult:            10,
			wantErr:               false,
			expectedCallbackCount: 4,
		},
		{
			name:  "error at third element stops iteration",
			input: []int{1, 2, 3, 4},
			accumulator: func(agg, item, _ int) (int, error) {
				if item == 3 {
					return 0, errors.New("number 3 is not allowed")
				}
				return agg + item, nil
			},
			initial:               0,
			wantResult:            0,
			wantErr:               true,
			errMsg:                "number 3 is not allowed",
			expectedCallbackCount: 3,
		},
		{
			name:  "error at first element stops iteration immediately",
			input: []int{1, 2, 3, 4},
			accumulator: func(agg, item, _ int) (int, error) {
				if item == 1 {
					return 0, errors.New("number 1 is not allowed")
				}
				return agg + item, nil
			},
			initial:               0,
			wantResult:            0,
			wantErr:               true,
			errMsg:                "number 1 is not allowed",
			expectedCallbackCount: 1,
		},
		{
			name:  "error at last element",
			input: []int{1, 2, 3, 4},
			accumulator: func(agg, item, _ int) (int, error) {
				if item == 4 {
					return 0, errors.New("number 4 is not allowed")
				}
				return agg + item, nil
			},
			initial:               0,
			wantResult:            0,
			wantErr:               true,
			errMsg:                "number 4 is not allowed",
			expectedCallbackCount: 4,
		},
		{
			name:  "empty input slice",
			input: []int{},
			accumulator: func(agg, item, _ int) (int, error) {
				return agg + item, nil
			},
			initial:               10,
			wantResult:            10,
			wantErr:               false,
			expectedCallbackCount: 0,
		},
		{
			name:  "with non-zero initial value",
			input: []int{1, 2, 3, 4},
			accumulator: func(agg, item, _ int) (int, error) {
				return agg + item, nil
			},
			initial:               10,
			wantResult:            20,
			wantErr:               false,
			expectedCallbackCount: 4,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			// Track callback count to test early return
			callbackCount := 0
			wrappedAccumulator := func(agg, item, index int) (int, error) {
				callbackCount++
				return tt.accumulator(agg, item, index)
			}

			result, err := ReduceErr(tt.input, wrappedAccumulator, tt.initial)

			if tt.wantErr {
				is.Error(err)
				is.Equal(tt.errMsg, err.Error())
			} else {
				is.NoError(err)
				is.Equal(tt.wantResult, result)
			}

			// Verify callback count matches expected
			is.Equal(tt.expectedCallbackCount, callbackCount, "callback count should match expected")
		})
	}
}

func TestReduceRight(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := ReduceRight([][]int{{0, 1}, {2, 3}, {4, 5}}, func(agg, item []int, _ int) []int {
		return append(agg, item...)
	}, []int{})

	is.Equal([]int{4, 5, 2, 3, 0, 1}, result1)

	type collection []int
	result3 := ReduceRight(collection{1, 2, 3, 4}, func(agg, item, _ int) int {
		return agg + item
	}, 10)
	is.Equal(20, result3)
}

func TestReduceRightErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	tests := []struct {
		name                  string
		input                 []int
		accumulator           func(agg, item, index int) (int, error)
		initial               int
		wantResult            int
		wantErr               bool
		errMsg                string
		expectedCallbackCount int
	}{
		{
			name:  "successful reduction",
			input: []int{1, 2, 3, 4},
			accumulator: func(agg, item, _ int) (int, error) {
				return agg + item, nil
			},
			initial:               0,
			wantResult:            10,
			wantErr:               false,
			expectedCallbackCount: 4,
		},
		{
			name:  "error at second element from right stops iteration",
			input: []int{1, 2, 3, 4},
			accumulator: func(agg, item, _ int) (int, error) {
				if item == 3 {
					return 0, errors.New("number 3 is not allowed")
				}
				return agg + item, nil
			},
			initial:               0,
			wantResult:            0,
			wantErr:               true,
			errMsg:                "number 3 is not allowed",
			expectedCallbackCount: 2,
		},
		{
			name:  "error at first element from right stops iteration immediately",
			input: []int{1, 2, 3, 4},
			accumulator: func(agg, item, _ int) (int, error) {
				if item == 4 {
					return 0, errors.New("number 4 is not allowed")
				}
				return agg + item, nil
			},
			initial:               0,
			wantResult:            0,
			wantErr:               true,
			errMsg:                "number 4 is not allowed",
			expectedCallbackCount: 1,
		},
		{
			name:  "error at last element from left",
			input: []int{1, 2, 3, 4},
			accumulator: func(agg, item, _ int) (int, error) {
				if item == 1 {
					return 0, errors.New("number 1 is not allowed")
				}
				return agg + item, nil
			},
			initial:               0,
			wantResult:            0,
			wantErr:               true,
			errMsg:                "number 1 is not allowed",
			expectedCallbackCount: 4,
		},
		{
			name:  "empty input slice",
			input: []int{},
			accumulator: func(agg, item, _ int) (int, error) {
				return agg + item, nil
			},
			initial:               10,
			wantResult:            10,
			wantErr:               false,
			expectedCallbackCount: 0,
		},
		{
			name:  "with non-zero initial value",
			input: []int{1, 2, 3, 4},
			accumulator: func(agg, item, _ int) (int, error) {
				return agg + item, nil
			},
			initial:               10,
			wantResult:            20,
			wantErr:               false,
			expectedCallbackCount: 4,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			// Track callback count to test early return
			callbackCount := 0
			wrappedAccumulator := func(agg, item, index int) (int, error) {
				callbackCount++
				return tt.accumulator(agg, item, index)
			}

			result, err := ReduceRightErr(tt.input, wrappedAccumulator, tt.initial)

			if tt.wantErr {
				is.Error(err)
				is.Equal(tt.errMsg, err.Error())
			} else {
				is.NoError(err)
				is.Equal(tt.wantResult, result)
			}

			// Verify callback count matches expected
			is.Equal(tt.expectedCallbackCount, callbackCount, "callback count should match expected")
		})
	}
}

func TestForEach(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	// check of callback is called for every element and in proper order

	callParams1 := []string{}
	callParams2 := []int{}

	ForEach([]string{"a", "b", "c"}, func(item string, i int) {
		callParams1 = append(callParams1, item)
		callParams2 = append(callParams2, i)
	})

	is.Equal([]string{"a", "b", "c"}, callParams1)
	is.Equal([]int{0, 1, 2}, callParams2)
	is.IsIncreasing(callParams2)
}

func TestForEachWhile(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	// check of callback is called for every element and in proper order

	var callParams1 []string
	var callParams2 []int

	ForEachWhile([]string{"a", "b", "c"}, func(item string, i int) bool {
		if item == "c" {
			return false
		}
		callParams1 = append(callParams1, item)
		callParams2 = append(callParams2, i)
		return true
	})

	is.Equal([]string{"a", "b"}, callParams1)
	is.Equal([]int{0, 1}, callParams2)
	is.IsIncreasing(callParams2)
}

func TestUniq(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Uniq([]int{1, 2, 2, 1})
	is.Equal([]int{1, 2}, result1)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Uniq(allStrings)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestUniqBy(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := UniqBy([]int{0, 1, 2, 3, 4, 5}, func(i int) int {
		return i % 3
	})
	is.Equal([]int{0, 1, 2}, result1)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := UniqBy(allStrings, func(i string) string {
		return i
	})
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestUniqByErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	tests := []struct {
		name                  string
		input                 []int
		iteratee              func(item int) (int, error)
		wantResult            []int
		wantErr               bool
		errMsg                string
		expectedCallbackCount int
	}{
		{
			name:  "successful uniq",
			input: []int{0, 1, 2, 3, 4, 5},
			iteratee: func(i int) (int, error) {
				return i % 3, nil
			},
			wantResult:            []int{0, 1, 2},
			wantErr:               false,
			expectedCallbackCount: 6,
		},
		{
			name:  "error at fourth element stops iteration",
			input: []int{0, 1, 2, 3, 4, 5},
			iteratee: func(i int) (int, error) {
				if i == 3 {
					return 0, errors.New("number 3 is not allowed")
				}
				return i % 3, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 3 is not allowed",
			expectedCallbackCount: 4,
		},
		{
			name:  "error at first element stops iteration immediately",
			input: []int{0, 1, 2, 3, 4, 5},
			iteratee: func(i int) (int, error) {
				if i == 0 {
					return 0, errors.New("number 0 is not allowed")
				}
				return i % 3, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 0 is not allowed",
			expectedCallbackCount: 1,
		},
		{
			name:  "error at last element",
			input: []int{0, 1, 2, 3, 4, 5},
			iteratee: func(i int) (int, error) {
				if i == 5 {
					return 0, errors.New("number 5 is not allowed")
				}
				return i % 3, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 5 is not allowed",
			expectedCallbackCount: 6,
		},
		{
			name:  "empty input slice",
			input: []int{},
			iteratee: func(i int) (int, error) {
				return i % 3, nil
			},
			wantResult:            []int{},
			wantErr:               false,
			expectedCallbackCount: 0,
		},
		{
			name:  "all duplicates",
			input: []int{1, 1, 1, 1},
			iteratee: func(i int) (int, error) {
				return i % 3, nil
			},
			wantResult:            []int{1},
			wantErr:               false,
			expectedCallbackCount: 4,
		},
		{
			name:  "no duplicates",
			input: []int{0, 1, 2, 3},
			iteratee: func(i int) (int, error) {
				return i, nil
			},
			wantResult:            []int{0, 1, 2, 3},
			wantErr:               false,
			expectedCallbackCount: 4,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			// Track callback count to test early return
			callbackCount := 0
			wrappedIteratee := func(item int) (int, error) {
				callbackCount++
				return tt.iteratee(item)
			}

			result, err := UniqByErr(tt.input, wrappedIteratee)

			if tt.wantErr {
				is.Error(err)
				is.Equal(tt.errMsg, err.Error())
				is.Nil(result)
			} else {
				is.NoError(err)
				is.Equal(tt.wantResult, result)
			}

			// Verify callback count matches expected
			is.Equal(tt.expectedCallbackCount, callbackCount, "callback count should match expected")
		})
	}
}

func TestGroupBy(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := GroupBy([]int{0, 1, 2, 3, 4, 5}, func(i int) int {
		return i % 3
	})
	is.Equal(map[int][]int{
		0: {0, 3},
		1: {1, 4},
		2: {2, 5},
	}, result1)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := GroupBy(allStrings, func(i string) int {
		return 42
	})
	is.IsType(nonempty[42], allStrings, "type preserved")
}

func TestGroupByErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	tests := []struct {
		name                  string
		input                 []int
		iteratee              func(item int) (int, error)
		wantResult            map[int][]int
		wantErr               bool
		errMsg                string
		expectedCallbackCount int
	}{
		{
			name:  "successful grouping",
			input: []int{0, 1, 2, 3, 4, 5},
			iteratee: func(i int) (int, error) {
				return i % 3, nil
			},
			wantResult: map[int][]int{
				0: {0, 3},
				1: {1, 4},
				2: {2, 5},
			},
			wantErr:               false,
			expectedCallbackCount: 6,
		},
		{
			name:  "error at fourth element stops iteration",
			input: []int{0, 1, 2, 3, 4, 5},
			iteratee: func(i int) (int, error) {
				if i == 3 {
					return 0, errors.New("number 3 is not allowed")
				}
				return i % 3, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 3 is not allowed",
			expectedCallbackCount: 4,
		},
		{
			name:  "error at first element stops iteration immediately",
			input: []int{0, 1, 2, 3, 4, 5},
			iteratee: func(i int) (int, error) {
				if i == 0 {
					return 0, errors.New("number 0 is not allowed")
				}
				return i % 3, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 0 is not allowed",
			expectedCallbackCount: 1,
		},
		{
			name:  "error at last element",
			input: []int{0, 1, 2, 3, 4, 5},
			iteratee: func(i int) (int, error) {
				if i == 5 {
					return 0, errors.New("number 5 is not allowed")
				}
				return i % 3, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 5 is not allowed",
			expectedCallbackCount: 6,
		},
		{
			name:  "empty input slice",
			input: []int{},
			iteratee: func(i int) (int, error) {
				return i % 3, nil
			},
			wantResult:            map[int][]int{},
			wantErr:               false,
			expectedCallbackCount: 0,
		},
		{
			name:  "all elements in same group",
			input: []int{3, 6, 9, 12},
			iteratee: func(i int) (int, error) {
				return 0, nil
			},
			wantResult: map[int][]int{
				0: {3, 6, 9, 12},
			},
			wantErr:               false,
			expectedCallbackCount: 4,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			// Track callback count to test early return
			callbackCount := 0
			wrappedIteratee := func(item int) (int, error) {
				callbackCount++
				return tt.iteratee(item)
			}

			result, err := GroupByErr(tt.input, wrappedIteratee)

			if tt.wantErr {
				is.Error(err)
				is.Equal(tt.errMsg, err.Error())
				is.Nil(result)
			} else {
				is.NoError(err)
				is.Equal(tt.wantResult, result)
			}

			// Verify callback count matches expected
			is.Equal(tt.expectedCallbackCount, callbackCount, "callback count should match expected")
		})
	}
}

func TestGroupByMap(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := GroupByMap([]int{0, 1, 2, 3, 4, 5}, func(i int) (int, string) {
		return i % 3, strconv.Itoa(i)
	})
	is.Equal(map[int][]string{
		0: {"0", "3"},
		1: {"1", "4"},
		2: {"2", "5"},
	}, result1)

	type myInt int
	type myInts []myInt
	result2 := GroupByMap(myInts{1, 0, 2, 3, 4, 5}, func(i myInt) (int, string) {
		return int(i % 3), strconv.Itoa(int(i))
	})
	is.Equal(map[int][]string{
		0: {"0", "3"},
		1: {"1", "4"},
		2: {"2", "5"},
	}, result2)

	type product struct {
		ID         int64
		CategoryID int64
	}
	products := []product{
		{ID: 1, CategoryID: 1},
		{ID: 2, CategoryID: 1},
		{ID: 3, CategoryID: 2},
		{ID: 4, CategoryID: 3},
		{ID: 5, CategoryID: 3},
	}
	result3 := GroupByMap(products, func(item product) (int64, string) {
		return item.CategoryID, "Product " + strconv.FormatInt(item.ID, 10)
	})
	is.Equal(map[int64][]string{
		1: {"Product 1", "Product 2"},
		2: {"Product 3"},
		3: {"Product 4", "Product 5"},
	}, result3)
}

func TestGroupByMapErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	tests := []struct {
		name                  string
		input                 []int
		transform             func(item int) (int, int, error)
		wantResult            map[int][]int
		wantErr               bool
		errMsg                string
		expectedCallbackCount int
	}{
		{
			name:  "successful grouping",
			input: []int{0, 1, 2, 3, 4, 5},
			transform: func(i int) (int, int, error) {
				return i % 3, i * 2, nil
			},
			wantResult: map[int][]int{
				0: {0, 6},
				1: {2, 8},
				2: {4, 10},
			},
			wantErr:               false,
			expectedCallbackCount: 6,
		},
		{
			name:  "error at fourth element stops iteration",
			input: []int{0, 1, 2, 3, 4, 5},
			transform: func(i int) (int, int, error) {
				if i == 3 {
					return 0, 0, errors.New("number 3 is not allowed")
				}
				return i % 3, i * 2, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 3 is not allowed",
			expectedCallbackCount: 4,
		},
		{
			name:  "error at first element stops iteration immediately",
			input: []int{0, 1, 2, 3, 4, 5},
			transform: func(i int) (int, int, error) {
				if i == 0 {
					return 0, 0, errors.New("number 0 is not allowed")
				}
				return i % 3, i * 2, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 0 is not allowed",
			expectedCallbackCount: 1,
		},
		{
			name:  "error at last element",
			input: []int{0, 1, 2, 3, 4, 5},
			transform: func(i int) (int, int, error) {
				if i == 5 {
					return 0, 0, errors.New("number 5 is not allowed")
				}
				return i % 3, i * 2, nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 5 is not allowed",
			expectedCallbackCount: 6,
		},
		{
			name:  "empty input slice",
			input: []int{},
			transform: func(i int) (int, int, error) {
				return i % 3, i * 2, nil
			},
			wantResult:            map[int][]int{},
			wantErr:               false,
			expectedCallbackCount: 0,
		},
		{
			name:  "all elements in same group",
			input: []int{3, 6, 9, 12},
			transform: func(i int) (int, int, error) {
				return 0, i, nil
			},
			wantResult: map[int][]int{
				0: {3, 6, 9, 12},
			},
			wantErr:               false,
			expectedCallbackCount: 4,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			// Track callback count to test early return
			callbackCount := 0
			wrappedTransform := func(item int) (int, int, error) {
				callbackCount++
				return tt.transform(item)
			}

			result, err := GroupByMapErr(tt.input, wrappedTransform)

			if tt.wantErr {
				is.Error(err)
				is.Equal(tt.errMsg, err.Error())
				is.Nil(result)
			} else {
				is.NoError(err)
				is.Equal(tt.wantResult, result)
			}

			// Verify callback count matches expected
			is.Equal(tt.expectedCallbackCount, callbackCount, "callback count should match expected")
		})
	}
}

func TestChunk(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Chunk([]int{0, 1, 2, 3, 4, 5}, 2)
	result2 := Chunk([]int{0, 1, 2, 3, 4, 5, 6}, 2)
	result3 := Chunk([]int{}, 2)
	result4 := Chunk([]int{0}, 2)

	is.Equal([][]int{{0, 1}, {2, 3}, {4, 5}}, result1)
	is.Equal([][]int{{0, 1}, {2, 3}, {4, 5}, {6}}, result2)
	is.Empty(result3)
	is.Equal([][]int{{0}}, result4)
	is.PanicsWithValue("lo.Chunk: size must be greater than 0", func() {
		Chunk([]int{0}, 0)
	})

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Chunk(allStrings, 2)
	is.IsType(nonempty[0], allStrings, "type preserved")

	// appending to a chunk should not affect original slice
	original := []int{0, 1, 2, 3, 4, 5}
	result5 := Chunk(original, 2)
	result5[0] = append(result5[0], 6)
	is.Equal([]int{0, 1, 2, 3, 4, 5}, original)
}

func TestWindow(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Window([]int{1, 2, 3, 4, 5}, 3)
	result2 := Window([]int{1, 2, 3, 4, 5, 6}, 3)
	result3 := Window([]int{1, 2}, 3)
	result4 := Window([]int{1, 2, 3}, 3)
	result5 := Window([]int{1, 2, 3, 4}, 1)

	is.Equal([][]int{{1, 2, 3}, {2, 3, 4}, {3, 4, 5}}, result1)
	is.Equal([][]int{{1, 2, 3}, {2, 3, 4}, {3, 4, 5}, {4, 5, 6}}, result2)
	is.Empty(result3)
	is.Equal([][]int{{1, 2, 3}}, result4)
	is.Equal([][]int{{1}, {2}, {3}, {4}}, result5)

	is.PanicsWithValue("lo.Window: size must be greater than 0", func() {
		Window([]int{1, 2, 3}, 0)
	})

	is.PanicsWithValue("lo.Window: size must be greater than 0", func() {
		Window([]int{1, 2, 3}, -1)
	})

	type myStrings []string
	allStrings := myStrings{"a", "b", "c", "d"}
	windows := Window(allStrings, 2)
	is.IsType(windows[0], allStrings, "type preserved")
	is.Equal(myStrings{"a", "b"}, windows[0])

	// appending to a window should not affect original slice
	original := []int{1, 2, 3, 4, 5}
	windows2 := Window(original, 3)
	windows2[0] = append(windows2[0], 6)
	is.Equal([]int{1, 2, 3, 4, 5}, original)
}

func TestSliding(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	// Overlapping windows (step < size)
	result1 := Sliding([]int{1, 2, 3, 4, 5, 6}, 3, 1)
	is.Equal([][]int{{1, 2, 3}, {2, 3, 4}, {3, 4, 5}, {4, 5, 6}}, result1)

	// Non-overlapping windows (step == size, like Chunk)
	result2 := Sliding([]int{1, 2, 3, 4, 5, 6}, 3, 3)
	is.Equal([][]int{{1, 2, 3}, {4, 5, 6}}, result2)

	// Step > size (skipping elements)
	result3 := Sliding([]int{1, 2, 3, 4, 5, 6, 7, 8}, 2, 3)
	is.Equal([][]int{{1, 2}, {4, 5}, {7, 8}}, result3)

	// Single element windows
	result4 := Sliding([]int{1, 2, 3, 4}, 1, 1)
	is.Equal([][]int{{1}, {2}, {3}, {4}}, result4)

	// Empty result when collection is too small
	result5 := Sliding([]int{1, 2}, 3, 1)
	is.Empty(result5)

	// Step 2, size 2
	result6 := Sliding([]int{1, 2, 3, 4, 5, 6}, 2, 2)
	is.Equal([][]int{{1, 2}, {3, 4}, {5, 6}}, result6)

	is.PanicsWithValue("lo.Sliding: size must be greater than 0", func() {
		Sliding([]int{1, 2, 3}, 0, 1)
	})

	is.PanicsWithValue("lo.Sliding: step must be greater than 0", func() {
		Sliding([]int{1, 2, 3}, 2, 0)
	})

	is.PanicsWithValue("lo.Sliding: step must be greater than 0", func() {
		Sliding([]int{1, 2, 3}, 2, -1)
	})

	type myStrings []string
	allStrings := myStrings{"a", "b", "c", "d", "e"}
	windows := Sliding(allStrings, 2, 2)
	is.IsType(windows[0], allStrings, "type preserved")
	is.Equal(myStrings{"a", "b"}, windows[0])

	// appending to a window should not affect original slice
	original := []int{1, 2, 3, 4, 5, 6}
	windows2 := Sliding(original, 2, 2)
	windows2[0] = append(windows2[0], 7)
	is.Equal([]int{1, 2, 3, 4, 5, 6}, original)
}

func TestPartitionBy(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	oddEven := func(x int) string {
		if x < 0 {
			return "negative"
		} else if x%2 == 0 {
			return "even"
		}
		return "odd"
	}

	result1 := PartitionBy([]int{-2, -1, 0, 1, 2, 3, 4, 5}, oddEven)
	result2 := PartitionBy([]int{}, oddEven)

	is.Equal([][]int{{-2, -1}, {0, 2, 4}, {1, 3, 5}}, result1)
	is.Empty(result2)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := PartitionBy(allStrings, func(item string) int {
		return len(item)
	})
	is.IsType(nonempty[0], allStrings, "type preserved")
}

func TestPartitionByErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	oddEven := func(x int) (string, error) {
		if x < 0 {
			return "negative", nil
		} else if x%2 == 0 {
			return "even", nil
		}
		return "odd", nil
	}

	tests := []struct {
		name                  string
		input                 []int
		iteratee              func(item int) (string, error)
		wantResult            [][]int
		wantErr               bool
		errMsg                string
		expectedCallbackCount int
	}{
		{
			name:                  "successful partition",
			input:                 []int{-2, -1, 0, 1, 2, 3, 4, 5},
			iteratee:              oddEven,
			wantResult:            [][]int{{-2, -1}, {0, 2, 4}, {1, 3, 5}},
			wantErr:               false,
			expectedCallbackCount: 8,
		},
		{
			name:  "error at fifth element stops iteration",
			input: []int{-2, -1, 0, 1, 2, 3},
			iteratee: func(x int) (string, error) {
				if x == 2 {
					return "", errors.New("number 2 is not allowed")
				}
				return oddEven(x)
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 2 is not allowed",
			expectedCallbackCount: 5,
		},
		{
			name:  "error at first element stops iteration immediately",
			input: []int{-2, -1, 0, 1},
			iteratee: func(x int) (string, error) {
				if x == -2 {
					return "", errors.New("number -2 is not allowed")
				}
				return oddEven(x)
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number -2 is not allowed",
			expectedCallbackCount: 1,
		},
		{
			name:  "error at last element",
			input: []int{-2, -1, 0, 1, 2},
			iteratee: func(x int) (string, error) {
				if x == 2 {
					return "", errors.New("number 2 is not allowed")
				}
				return oddEven(x)
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "number 2 is not allowed",
			expectedCallbackCount: 5,
		},
		{
			name:                  "empty input slice",
			input:                 []int{},
			iteratee:              oddEven,
			wantResult:            [][]int{},
			wantErr:               false,
			expectedCallbackCount: 0,
		},
		{
			name:  "all elements in same partition",
			input: []int{1, 3, 5},
			iteratee: func(x int) (string, error) {
				return "odd", nil
			},
			wantResult:            [][]int{{1, 3, 5}},
			wantErr:               false,
			expectedCallbackCount: 3,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			// Track callback count to test early return
			callbackCount := 0
			wrappedIteratee := func(item int) (string, error) {
				callbackCount++
				return tt.iteratee(item)
			}

			result, err := PartitionByErr(tt.input, wrappedIteratee)

			if tt.wantErr {
				is.Error(err)
				is.Equal(tt.errMsg, err.Error())
				is.Nil(result)
			} else {
				is.NoError(err)
				is.Equal(tt.wantResult, result)
			}

			// Verify callback count matches expected
			is.Equal(tt.expectedCallbackCount, callbackCount, "callback count should match expected")
		})
	}
}

func TestFlatten(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Flatten([][]int{{0, 1}, {2, 3, 4, 5}})

	is.Equal([]int{0, 1, 2, 3, 4, 5}, result1)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Flatten([]myStrings{allStrings})
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestConcat(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Concat([][]int{{0, 1}, {2, 3, 4, 5}}...)

	is.Equal([]int{0, 1, 2, 3, 4, 5}, result1)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Concat([]myStrings{allStrings}...)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestInterleave(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	testCases := []struct {
		name string
		in   [][]int
		want []int
	}{
		{
			"nil",
			[][]int{nil},
			[]int{},
		},
		{
			"empty",
			[][]int{},
			[]int{},
		},
		{
			"empties",
			[][]int{{}, {}},
			[]int{},
		},
		{
			"same length",
			[][]int{{1, 3, 5}, {2, 4, 6}},
			[]int{1, 2, 3, 4, 5, 6},
		},
		{
			"different length",
			[][]int{{1, 3, 5, 6}, {2, 4}},
			[]int{1, 2, 3, 4, 5, 6},
		},
		{
			"many slices",
			[][]int{{1}, {2, 5, 8}, {3, 6}, {4, 7, 9, 10}},
			[]int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10},
		},
	}
	for _, tc := range testCases {
		tc := tc
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()
			assert.Equal(t, tc.want, Interleave(tc.in...))
		})
	}

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Interleave(allStrings)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestShuffle(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Shuffle([]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10})
	result2 := Shuffle([]int{})

	is.NotEqual([]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, result1)
	is.ElementsMatch([]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, result1)
	is.Empty(result2)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Shuffle(allStrings)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestReverse(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Reverse([]int{0, 1, 2, 3, 4, 5})
	result2 := Reverse([]int{0, 1, 2, 3, 4, 5, 6})
	result3 := Reverse([]int{})

	is.Equal([]int{5, 4, 3, 2, 1, 0}, result1)
	is.Equal([]int{6, 5, 4, 3, 2, 1, 0}, result2)
	is.Empty(result3)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Reverse(allStrings)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestFill(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Fill([]foo{{"a"}, {"a"}}, foo{"b"})
	result2 := Fill([]foo{}, foo{"a"})

	is.Equal([]foo{{"b"}, {"b"}}, result1)
	is.Empty(result2)
}

func TestRepeat(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Repeat(2, foo{"a"})
	result2 := Repeat(0, foo{"a"})

	is.Equal([]foo{{"a"}, {"a"}}, result1)
	is.Empty(result2)
}

func TestRepeatBy(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	cb := func(i int) int {
		return int(math.Pow(float64(i), 2))
	}

	result1 := RepeatBy(0, cb)
	result2 := RepeatBy(2, cb)
	result3 := RepeatBy(5, cb)

	is.Empty(result1)
	is.Equal([]int{0, 1}, result2)
	is.Equal([]int{0, 1, 4, 9, 16}, result3)
}

func TestRepeatByErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	testErr := errors.New("test error")

	// Table-driven tests
	tests := []struct {
		name                  string
		count                 int
		callback              func(index int) (int, error)
		wantResult            []int
		wantErr               bool
		expectedCallbackCount int
	}{
		{
			name:  "successful completion",
			count: 5,
			callback: func(i int) (int, error) {
				return i * i, nil
			},
			wantResult:            []int{0, 1, 4, 9, 16},
			wantErr:               false,
			expectedCallbackCount: 5,
		},
		{
			name:  "error at first iteration",
			count: 5,
			callback: func(i int) (int, error) {
				if i == 0 {
					return 0, testErr
				}
				return i * i, nil
			},
			wantResult:            nil,
			wantErr:               true,
			expectedCallbackCount: 1,
		},
		{
			name:  "error at third iteration",
			count: 5,
			callback: func(i int) (int, error) {
				if i == 2 {
					return 0, testErr
				}
				return i * i, nil
			},
			wantResult:            nil,
			wantErr:               true,
			expectedCallbackCount: 3,
		},
		{
			name:  "error at last iteration",
			count: 5,
			callback: func(i int) (int, error) {
				if i == 4 {
					return 0, testErr
				}
				return i * i, nil
			},
			wantResult:            nil,
			wantErr:               true,
			expectedCallbackCount: 5,
		},
		{
			name:  "zero count - empty result",
			count: 0,
			callback: func(i int) (int, error) {
				return i * i, nil
			},
			wantResult:            []int{},
			wantErr:               false,
			expectedCallbackCount: 0,
		},
		{
			name:  "single item success",
			count: 1,
			callback: func(i int) (int, error) {
				return 42, nil
			},
			wantResult:            []int{42},
			wantErr:               false,
			expectedCallbackCount: 1,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			// Track callback count to verify early return
			callbackCount := 0
			wrappedCallback := func(i int) (int, error) {
				callbackCount++
				return tt.callback(i)
			}

			result, err := RepeatByErr(tt.count, wrappedCallback)

			if tt.wantErr {
				is.ErrorIs(err, testErr)
				is.Nil(result)
			} else {
				is.NoError(err)
				is.Equal(tt.wantResult, result)
			}

			// Verify callback count matches expected (tests early return)
			is.Equal(tt.expectedCallbackCount, callbackCount, "callback count should match expected")
		})
	}
}

func TestKeyBy(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := KeyBy([]string{"a", "aa", "aaa"}, func(str string) int {
		return len(str)
	})

	is.Equal(map[int]string{1: "a", 2: "aa", 3: "aaa"}, result1)
}

func TestKeyByErr(t *testing.T) {
	t.Parallel()

	tests := []struct {
		name                  string
		input                 []string
		iteratee              func(item string) (int, error)
		wantResult            map[int]string
		wantErr               bool
		errMsg                string
		expectedCallbackCount int
	}{
		{
			name:                  "empty slice",
			input:                 []string{},
			iteratee:              func(s string) (int, error) { return len(s), nil },
			wantResult:            map[int]string{},
			wantErr:               false,
			expectedCallbackCount: 0,
		},
		{
			name:                  "success case",
			input:                 []string{"a", "aa", "aaa"},
			iteratee:              func(s string) (int, error) { return len(s), nil },
			wantResult:            map[int]string{1: "a", 2: "aa", 3: "aaa"},
			wantErr:               false,
			expectedCallbackCount: 3,
		},
		{
			name:  "error stops iteration - first item",
			input: []string{"a", "aa", "aaa"},
			iteratee: func(s string) (int, error) {
				return 0, fmt.Errorf("error on %s", s)
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "error on a",
			expectedCallbackCount: 1,
		},
		{
			name:  "error stops iteration - middle item",
			input: []string{"a", "aa", "aaa"},
			iteratee: func(s string) (int, error) {
				if s == "aa" {
					return 0, errors.New("middle error")
				}
				return len(s), nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "middle error",
			expectedCallbackCount: 2,
		},
		{
			name:  "error stops iteration - last item",
			input: []string{"a", "aa", "aaa"},
			iteratee: func(s string) (int, error) {
				if s == "aaa" {
					return 0, errors.New("last error")
				}
				return len(s), nil
			},
			wantResult:            nil,
			wantErr:               true,
			errMsg:                "last error",
			expectedCallbackCount: 3,
		},
		{
			name:                  "duplicate keys",
			input:                 []string{"a", "b", "c"},
			iteratee:              func(s string) (int, error) { return 1, nil },
			wantResult:            map[int]string{1: "c"},
			wantErr:               false,
			expectedCallbackCount: 3,
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			callbackCount := 0
			wrappedIteratee := func(s string) (int, error) {
				callbackCount++
				return tt.iteratee(s)
			}

			result, err := KeyByErr(tt.input, wrappedIteratee)

			if tt.wantErr {
				assert.Error(t, err)
				if tt.errMsg != "" {
					assert.Equal(t, tt.errMsg, err.Error())
				}
				assert.Nil(t, result)
			} else {
				assert.NoError(t, err)
				assert.Equal(t, tt.wantResult, result)
			}

			assert.Equal(t, tt.expectedCallbackCount, callbackCount, "callback count mismatch")
		})
	}
}

func TestAssociate(t *testing.T) {
	t.Parallel()

	type foo struct {
		baz string
		bar int
	}
	transform := func(f *foo) (string, int) {
		return f.baz, f.bar
	}
	testCases := []struct {
		in   []*foo
		want map[string]int
	}{
		{
			in:   []*foo{{baz: "apple", bar: 1}},
			want: map[string]int{"apple": 1},
		},
		{
			in:   []*foo{{baz: "apple", bar: 1}, {baz: "banana", bar: 2}},
			want: map[string]int{"apple": 1, "banana": 2},
		},
		{
			in:   []*foo{{baz: "apple", bar: 1}, {baz: "apple", bar: 2}},
			want: map[string]int{"apple": 2},
		},
	}
	for i, tc := range testCases {
		tc := tc
		t.Run(fmt.Sprintf("test_%d", i), func(t *testing.T) {
			t.Parallel()
			assert.Equal(t, tc.want, Associate(tc.in, transform))
		})
	}
}

func TestAssociateI(t *testing.T) {
	t.Parallel()

	transform := func(s string, i int) (int, string) {
		return i % 2, s
	}
	testCases := []struct {
		in   []string
		want map[int]string
	}{
		{
			in:   []string{"zero"},
			want: map[int]string{0: "zero"},
		},
		{
			in:   []string{"zero", "one"},
			want: map[int]string{0: "zero", 1: "one"},
		},
		{
			in:   []string{"two", "one", "zero"},
			want: map[int]string{0: "zero", 1: "one"},
		},
	}
	for i, tc := range testCases {
		tc := tc
		t.Run(fmt.Sprintf("test_%d", i), func(t *testing.T) {
			t.Parallel()
			assert.Equal(t, tc.want, AssociateI(tc.in, transform))
		})
	}
}

func TestSliceToMap(t *testing.T) {
	t.Parallel()

	type foo struct {
		baz string
		bar int
	}
	transform := func(f *foo) (string, int) {
		return f.baz, f.bar
	}
	testCases := []struct {
		in   []*foo
		want map[string]int
	}{
		{
			in:   []*foo{{baz: "apple", bar: 1}},
			want: map[string]int{"apple": 1},
		},
		{
			in:   []*foo{{baz: "apple", bar: 1}, {baz: "banana", bar: 2}},
			want: map[string]int{"apple": 1, "banana": 2},
		},
		{
			in:   []*foo{{baz: "apple", bar: 1}, {baz: "apple", bar: 2}},
			want: map[string]int{"apple": 2},
		},
	}
	for i, tc := range testCases {
		tc := tc
		t.Run(fmt.Sprintf("test_%d", i), func(t *testing.T) {
			t.Parallel()
			assert.Equal(t, tc.want, SliceToMap(tc.in, transform))
		})
	}
}

func TestSliceToMapI(t *testing.T) {
	t.Parallel()

	transform := func(s string, i int) (int, string) {
		return i % 2, s
	}
	testCases := []struct {
		in   []string
		want map[int]string
	}{
		{
			in:   []string{"zero"},
			want: map[int]string{0: "zero"},
		},
		{
			in:   []string{"zero", "one"},
			want: map[int]string{0: "zero", 1: "one"},
		},
		{
			in:   []string{"two", "one", "zero"},
			want: map[int]string{0: "zero", 1: "one"},
		},
	}
	for i, tc := range testCases {
		tc := tc
		t.Run(fmt.Sprintf("test_%d", i), func(t *testing.T) {
			t.Parallel()
			assert.Equal(t, tc.want, SliceToMapI(tc.in, transform))
		})
	}
}

func TestFilterSliceToMap(t *testing.T) {
	t.Parallel()

	type foo struct {
		baz string
		bar int
	}
	transform := func(f *foo) (string, int, bool) {
		return f.baz, f.bar, f.bar > 1
	}
	testCases := []struct {
		in   []*foo
		want map[string]int
	}{
		{
			in:   []*foo{{baz: "apple", bar: 1}},
			want: map[string]int{},
		},
		{
			in:   []*foo{{baz: "apple", bar: 1}, {baz: "banana", bar: 2}},
			want: map[string]int{"banana": 2},
		},
		{
			in:   []*foo{{baz: "apple", bar: 1}, {baz: "apple", bar: 2}},
			want: map[string]int{"apple": 2},
		},
	}
	for i, tc := range testCases {
		tc := tc
		t.Run(fmt.Sprintf("test_%d", i), func(t *testing.T) {
			t.Parallel()
			assert.Equal(t, tc.want, FilterSliceToMap(tc.in, transform))
		})
	}
}

func TestFilterSliceToMapI(t *testing.T) {
	t.Parallel()

	transform := func(s string, i int) (int, string, bool) {
		return i % 5, s, i%2 == 0
	}
	testCases := []struct {
		in   []string
		want map[int]string
	}{
		{
			in:   []string{"zero"},
			want: map[int]string{0: "zero"},
		},
		{
			in:   []string{"zero", "one", "two", "three", "four"},
			want: map[int]string{0: "zero", 2: "two", 4: "four"},
		},
		{
			in:   []string{"zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", "ten"},
			want: map[int]string{0: "ten", 1: "six", 2: "two", 3: "eight", 4: "four"},
		},
	}
	for i, tc := range testCases {
		tc := tc
		t.Run(fmt.Sprintf("test_%d", i), func(t *testing.T) {
			t.Parallel()
			assert.Equal(t, tc.want, FilterSliceToMapI(tc.in, transform))
		})
	}
}

func TestKeyify(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	result1 := Keyify([]int{1, 2, 3, 4})
	result2 := Keyify([]int{1, 1, 1, 2})
	result3 := Keyify([]int{})
	is.Equal(map[int]struct{}{1: {}, 2: {}, 3: {}, 4: {}}, result1)
	is.Equal(map[int]struct{}{1: {}, 2: {}}, result2)
	is.Empty(result3)
}

func TestDrop(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.Equal([]int{0, 1, 2, 3, 4}, Drop([]int{0, 1, 2, 3, 4}, 0))
	is.Equal([]int{1, 2, 3, 4}, Drop([]int{0, 1, 2, 3, 4}, 1))
	is.Equal([]int{2, 3, 4}, Drop([]int{0, 1, 2, 3, 4}, 2))
	is.Equal([]int{3, 4}, Drop([]int{0, 1, 2, 3, 4}, 3))
	is.Equal([]int{4}, Drop([]int{0, 1, 2, 3, 4}, 4))
	is.Empty(Drop([]int{0, 1, 2, 3, 4}, 5))
	is.Empty(Drop([]int{0, 1, 2, 3, 4}, 6))

	is.PanicsWithValue("lo.Drop: n must not be negative", func() {
		Drop([]int{0, 1, 2, 3, 4}, -1)
	})

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Drop(allStrings, 2)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestDropRight(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.Equal([]int{0, 1, 2, 3, 4}, DropRight([]int{0, 1, 2, 3, 4}, 0))
	is.Equal([]int{0, 1, 2, 3}, DropRight([]int{0, 1, 2, 3, 4}, 1))
	is.Equal([]int{0, 1, 2}, DropRight([]int{0, 1, 2, 3, 4}, 2))
	is.Equal([]int{0, 1}, DropRight([]int{0, 1, 2, 3, 4}, 3))
	is.Equal([]int{0}, DropRight([]int{0, 1, 2, 3, 4}, 4))
	is.Empty(DropRight([]int{0, 1, 2, 3, 4}, 5))
	is.Empty(DropRight([]int{0, 1, 2, 3, 4}, 6))

	is.PanicsWithValue("lo.DropRight: n must not be negative", func() {
		DropRight([]int{0, 1, 2, 3, 4}, -1)
	})

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := DropRight(allStrings, 2)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestDropWhile(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.Equal([]int{4, 5, 6}, DropWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return t != 4
	}))

	is.Empty(DropWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return true
	}))

	is.Equal([]int{0, 1, 2, 3, 4, 5, 6}, DropWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return t == 10
	}))

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := DropWhile(allStrings, func(t string) bool {
		return t != "foo"
	})
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestDropRightWhile(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.Equal([]int{0, 1, 2, 3}, DropRightWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return t != 3
	}))

	is.Equal([]int{0, 1}, DropRightWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return t != 1
	}))

	is.Equal([]int{0, 1, 2, 3, 4, 5, 6}, DropRightWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return t == 10
	}))

	is.Empty(DropRightWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return t != 10
	}))

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := DropRightWhile(allStrings, func(t string) bool {
		return t != "foo"
	})
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestTake(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.Equal([]int{0, 1, 2}, Take([]int{0, 1, 2, 3, 4}, 3))
	is.Equal([]int{0, 1}, Take([]int{0, 1, 2, 3, 4}, 2))
	is.Equal([]int{0}, Take([]int{0, 1, 2, 3, 4}, 1))
	is.Empty(Take([]int{0, 1, 2, 3, 4}, 0))
	is.Equal([]int{0, 1, 2, 3, 4}, Take([]int{0, 1, 2, 3, 4}, 5))
	is.Equal([]int{0, 1, 2, 3, 4}, Take([]int{0, 1, 2, 3, 4}, 10))

	is.PanicsWithValue("lo.Take: n must not be negative", func() {
		Take([]int{0, 1, 2, 3, 4}, -1)
	})

	type myStrings []string
	allStrings := myStrings{"foo", "bar", "baz"}
	taken := Take(allStrings, 2)
	is.IsType(taken, allStrings, "type preserved")
	is.Equal(myStrings{"foo", "bar"}, taken)
}

func TestTakeWhile(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.Equal([]int{0, 1, 2, 3}, TakeWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return t < 4
	}))

	is.Equal([]int{0, 1, 2, 3, 4, 5, 6}, TakeWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return t < 10
	}))

	is.Empty(TakeWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return t < 0
	}))

	is.Equal([]int{0, 1, 2}, TakeWhile([]int{0, 1, 2, 3, 4, 5, 6}, func(t int) bool {
		return t != 3
	}))

	type myStrings []string
	allStrings := myStrings{"foo", "bar", "baz", "qux"}
	taken := TakeWhile(allStrings, func(t string) bool {
		return t != "baz"
	})
	is.IsType(taken, allStrings, "type preserved")
	is.Equal(myStrings{"foo", "bar"}, taken)
}

func TestTakeFilter(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.Equal(
		[]int{2, 4}, TakeFilter([]int{1, 2, 3, 4, 5, 6}, 2, func(item, index int) bool {
			return item%2 == 0
		}),
	)

	is.Equal([]int{2, 4, 6}, TakeFilter([]int{1, 2, 3, 4, 5, 6}, 10, func(item, index int) bool {
		return item%2 == 0
	}))

	is.Empty(TakeFilter([]int{1, 2, 3, 4, 5, 6}, 0, func(item, index int) bool {
		return item%2 == 0
	}))

	is.Empty(TakeFilter([]int{1, 3, 5}, 2, func(item, index int) bool {
		return item%2 == 0
	}))

	is.Equal([]int{1}, TakeFilter([]int{1, 2, 3, 4, 5}, 1, func(item, index int) bool {
		return item%2 != 0
	}))

	is.PanicsWithValue("lo.TakeFilter: n must not be negative", func() {
		TakeFilter([]int{1, 2, 3}, -1, func(item, index int) bool { return true })
	})

	type myStrings []string
	allStrings := myStrings{"foo", "bar", "baz", "qux"}
	filtered := TakeFilter(allStrings, 2, func(item string, index int) bool {
		return len(item) == 3
	})
	is.IsType(filtered, allStrings, "type preserved")
	is.Equal(myStrings{"foo", "bar"}, filtered)
}

func TestDropByIndex(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.Equal([]int{1, 2, 3, 4}, DropByIndex([]int{0, 1, 2, 3, 4}, 0))
	is.Equal([]int{3, 4}, DropByIndex([]int{0, 1, 2, 3, 4}, 0, 1, 2))
	is.Equal([]int{0, 4}, DropByIndex([]int{0, 1, 2, 3, 4}, -4, -2, -3))
	is.Equal([]int{0, 2, 3, 4}, DropByIndex([]int{0, 1, 2, 3, 4}, -4, -4))
	is.Equal([]int{2, 4}, DropByIndex([]int{0, 1, 2, 3, 4}, 3, 1, 0))
	is.Equal([]int{0, 1, 3, 4}, DropByIndex([]int{0, 1, 2, 3, 4}, 2))
	is.Equal([]int{0, 1, 2, 3}, DropByIndex([]int{0, 1, 2, 3, 4}, 4))
	is.Equal([]int{0, 1, 2, 3, 4}, DropByIndex([]int{0, 1, 2, 3, 4}))
	is.Equal([]int{0, 1, 2, 3, 4}, DropByIndex([]int{0, 1, 2, 3, 4}, 5))
	is.Equal([]int{0, 1, 2, 3, 4}, DropByIndex([]int{0, 1, 2, 3, 4}, 100))
	is.Equal([]int{0, 1, 2, 3, 4}, DropByIndex([]int{0, 1, 2, 3, 4}, -100))
	is.Equal([]int{0, 1, 2, 3}, DropByIndex([]int{0, 1, 2, 3, 4}, -1))
	is.Equal([]int{0, 1, 2, 3}, DropByIndex([]int{0, 1, 2, 3, 4}, -1, 4))
	is.Equal([]int{0, 1, 2, 3}, DropByIndex([]int{0, 1, 2, 3, 4}, -100, 4))
	is.Empty(DropByIndex([]int{}, 0, 1))
	is.Empty(DropByIndex([]int{42}, 0, 1))
	is.Empty(DropByIndex([]int{42}, 1, 0))
	is.Empty(DropByIndex([]int{}, 1))
	is.Empty(DropByIndex([]int{1}, 0))

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := DropByIndex(allStrings, 0)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestReject(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	r1 := Reject([]int{1, 2, 3, 4}, func(x, _ int) bool {
		return x%2 == 0
	})

	is.Equal([]int{1, 3}, r1)

	r2 := Reject([]string{"Smith", "foo", "Domin", "bar", "Olivia"}, func(x string, _ int) bool {
		return len(x) > 3
	})

	is.Equal([]string{"foo", "bar"}, r2)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Reject(allStrings, func(x string, _ int) bool {
		return len(x) > 0
	})
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestRejectErr(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	tests := []struct {
		name      string
		input     []int
		predicate func(item, index int) (bool, error)
		want      []int
		wantErr   string
		callbacks int // Number of predicates called before error/finish
	}{
		{
			name:  "reject even numbers",
			input: []int{1, 2, 3, 4},
			predicate: func(x, _ int) (bool, error) {
				return x%2 == 0, nil
			},
			want:      []int{1, 3},
			callbacks: 4,
		},
		{
			name:  "empty slice",
			input: []int{},
			predicate: func(x, _ int) (bool, error) {
				return true, nil
			},
			want:      []int{},
			callbacks: 0,
		},
		{
			name:  "reject all out",
			input: []int{1, 2, 3, 4},
			predicate: func(x, _ int) (bool, error) {
				return false, nil
			},
			want:      []int{1, 2, 3, 4},
			callbacks: 4,
		},
		{
			name:  "reject all in",
			input: []int{1, 2, 3, 4},
			predicate: func(x, _ int) (bool, error) {
				return true, nil
			},
			want:      []int{},
			callbacks: 4,
		},
		{
			name:  "error on specific index",
			input: []int{1, 2, 3, 4},
			predicate: func(x, _ int) (bool, error) {
				if x == 3 {
					return false, errors.New("number 3 is not allowed")
				}
				return x%2 == 0, nil
			},
			callbacks: 3,
			wantErr:   "number 3 is not allowed",
		},
	}

	for _, tt := range tests {
		tt := tt
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			var callbacks int
			wrappedPredicate := func(item, index int) (bool, error) {
				callbacks++
				return tt.predicate(item, index)
			}

			got, err := RejectErr(tt.input, wrappedPredicate)

			if tt.wantErr != "" {
				is.Error(err)
				is.Equal(tt.wantErr, err.Error())
				is.Nil(got)
				is.Equal(tt.callbacks, callbacks, "callback count should match expected early return")
			} else {
				is.NoError(err)
				is.Equal(tt.want, got)
				is.Equal(tt.callbacks, callbacks)
			}
		})
	}

	// Test type preservation
	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty, err := RejectErr(allStrings, func(x string, _ int) (bool, error) {
		return len(x) > 0, nil
	})
	is.NoError(err)
	is.IsType(nonempty, allStrings, "type preserved")
	is.Equal(myStrings{""}, nonempty)
}

func TestRejectMap(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	r1 := RejectMap([]int64{1, 2, 3, 4}, func(x int64, _ int) (string, bool) {
		if x%2 == 0 {
			return strconv.FormatInt(x, 10), false
		}
		return "", true
	})
	r2 := RejectMap([]string{"cpu", "gpu", "mouse", "keyboard"}, func(x string, _ int) (string, bool) {
		if strings.HasSuffix(x, "pu") {
			return "xpu", false
		}
		return "", true
	})

	is.Equal([]string{"2", "4"}, r1)
	is.Equal([]string{"xpu", "xpu"}, r2)
}

func TestFilterReject(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	left1, right1 := FilterReject([]int{1, 2, 3, 4}, func(x, _ int) bool {
		return x%2 == 0
	})

	is.Equal([]int{2, 4}, left1)
	is.Equal([]int{1, 3}, right1)

	left2, right2 := FilterReject([]string{"Smith", "foo", "Domin", "bar", "Olivia"}, func(x string, _ int) bool {
		return len(x) > 3
	})

	is.Equal([]string{"Smith", "Domin", "Olivia"}, left2)
	is.Equal([]string{"foo", "bar"}, right2)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	a, b := FilterReject(allStrings, func(x string, _ int) bool {
		return len(x) > 0
	})
	is.IsType(a, allStrings, "type preserved")
	is.IsType(b, allStrings, "type preserved")
}

func TestCount(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	count1 := Count([]int{1, 2, 1}, 1)
	count2 := Count([]int{1, 2, 1}, 3)
	count3 := Count([]int{}, 1)

	is.Equal(2, count1)
	is.Zero(count2)
	is.Zero(count3)
}

func TestCountBy(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	count1 := CountBy([]int{1, 2, 1}, func(i int) bool {
		return i < 2
	})

	count2 := CountBy([]int{1, 2, 1}, func(i int) bool {
		return i > 2
	})

	count3 := CountBy([]int{}, func(i int) bool {
		return i <= 2
	})

	is.Equal(2, count1)
	is.Zero(count2)
	is.Zero(count3)
}

func TestCountByErr(t *testing.T) {
	t.Parallel()

	tests := []struct {
		name          string
		input         []int
		predicate     func(int) (bool, error)
		want          int
		wantErr       string
		wantCallCount int
	}{
		{
			name:  "count elements less than 2",
			input: []int{1, 2, 1},
			predicate: func(i int) (bool, error) {
				return i < 2, nil
			},
			want:          2,
			wantErr:       "",
			wantCallCount: 3,
		},
		{
			name:  "count elements greater than 2",
			input: []int{1, 2, 1},
			predicate: func(i int) (bool, error) {
				return i > 2, nil
			},
			want:          0,
			wantErr:       "",
			wantCallCount: 3,
		},
		{
			name:  "empty slice",
			input: []int{},
			predicate: func(i int) (bool, error) {
				return i <= 2, nil
			},
			want:          0,
			wantErr:       "",
			wantCallCount: 0,
		},
		{
			name:  "error on third element",
			input: []int{1, 2, 3, 4, 5},
			predicate: func(i int) (bool, error) {
				if i == 3 {
					return false, fmt.Errorf("error at %d", i)
				}
				return i < 3, nil
			},
			want:          0,
			wantErr:       "error at 3",
			wantCallCount: 3, // stops early at error
		},
		{
			name:  "error on first element",
			input: []int{1, 2, 3},
			predicate: func(i int) (bool, error) {
				return false, errors.New("first element error")
			},
			want:          0,
			wantErr:       "first element error",
			wantCallCount: 1,
		},
		{
			name:  "all match",
			input: []int{1, 2, 3},
			predicate: func(i int) (bool, error) {
				return i > 0, nil
			},
			want:          3,
			wantErr:       "",
			wantCallCount: 3,
		},
	}

	for _, tt := range tests {
		tt := tt // capture range variable
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()
			is := assert.New(t)

			callCount := 0
			wrappedPredicate := func(i int) (bool, error) {
				callCount++
				return tt.predicate(i)
			}

			got, err := CountByErr(tt.input, wrappedPredicate)

			if tt.wantErr != "" {
				is.Error(err)
				is.Equal(tt.wantErr, err.Error())
				is.Equal(tt.want, got)
				if tt.wantCallCount > 0 {
					is.Equal(tt.wantCallCount, callCount, "should stop early on error")
				}
			} else {
				is.NoError(err)
				is.Equal(tt.want, got)
				is.Equal(tt.wantCallCount, callCount)
			}
		})
	}
}

func TestCountValues(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.Empty(CountValues([]int{}))
	is.Equal(map[int]int{1: 1, 2: 1}, CountValues([]int{1, 2}))
	is.Equal(map[int]int{1: 1, 2: 2}, CountValues([]int{1, 2, 2}))
	is.Equal(map[string]int{"": 1, "foo": 1, "bar": 1}, CountValues([]string{"foo", "bar", ""}))
	is.Equal(map[string]int{"foo": 1, "bar": 2}, CountValues([]string{"foo", "bar", "bar"}))
}

func TestCountValuesBy(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	oddEven := func(v int) bool {
		return v%2 == 0
	}
	length := func(v string) int {
		return len(v)
	}

	result1 := CountValuesBy([]int{}, oddEven)
	result2 := CountValuesBy([]int{1, 2}, oddEven)
	result3 := CountValuesBy([]int{1, 2, 2}, oddEven)
	result4 := CountValuesBy([]string{"foo", "bar", ""}, length)
	result5 := CountValuesBy([]string{"foo", "bar", "bar"}, length)

	is.Empty(result1)
	is.Equal(map[bool]int{true: 1, false: 1}, result2)
	is.Equal(map[bool]int{true: 2, false: 1}, result3)
	is.Equal(map[int]int{0: 1, 3: 2}, result4)
	is.Equal(map[int]int{3: 3}, result5)
}

func TestSubset(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	in := []int{0, 1, 2, 3, 4}

	out1 := Subset(in, 0, 0)
	out2 := Subset(in, 10, 2)
	out3 := Subset(in, -10, 2)
	out4 := Subset(in, 0, 10)
	out5 := Subset(in, 0, 2)
	out6 := Subset(in, 2, 2)
	out7 := Subset(in, 2, 5)
	out8 := Subset(in, 2, 3)
	out9 := Subset(in, 2, 4)
	out10 := Subset(in, -2, 4)
	out11 := Subset(in, -4, 1)
	out12 := Subset(in, -4, math.MaxUint)

	is.Empty(out1)
	is.Empty(out2)
	is.Equal([]int{0, 1}, out3)
	is.Equal([]int{0, 1, 2, 3, 4}, out4)
	is.Equal([]int{0, 1}, out5)
	is.Equal([]int{2, 3}, out6)
	is.Equal([]int{2, 3, 4}, out7)
	is.Equal([]int{2, 3, 4}, out8)
	is.Equal([]int{2, 3, 4}, out9)
	is.Equal([]int{3, 4}, out10)
	is.Equal([]int{1}, out11)
	is.Equal([]int{1, 2, 3, 4}, out12)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Subset(allStrings, 0, 2)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestSlice(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	in := []int{0, 1, 2, 3, 4}

	out1 := Slice(in, 0, 0)
	out2 := Slice(in, 0, 1)
	out3 := Slice(in, 0, 5)
	out4 := Slice(in, 0, 6)
	out5 := Slice(in, 1, 1)
	out6 := Slice(in, 1, 5)
	out7 := Slice(in, 1, 6)
	out8 := Slice(in, 4, 5)
	out9 := Slice(in, 5, 5)
	out10 := Slice(in, 6, 5)
	out11 := Slice(in, 6, 6)
	out12 := Slice(in, 1, 0)
	out13 := Slice(in, 5, 0)
	out14 := Slice(in, 6, 4)
	out15 := Slice(in, 6, 7)
	out16 := Slice(in, -10, 1)
	out17 := Slice(in, -1, 3)
	out18 := Slice(in, -10, 7)
	out19 := Slice(in, -10, -1)

	is.Empty(out1)
	is.Equal([]int{0}, out2)
	is.Equal([]int{0, 1, 2, 3, 4}, out3)
	is.Equal([]int{0, 1, 2, 3, 4}, out4)
	is.Empty(out5)
	is.Equal([]int{1, 2, 3, 4}, out6)
	is.Equal([]int{1, 2, 3, 4}, out7)
	is.Equal([]int{4}, out8)
	is.Empty(out9)
	is.Empty(out10)
	is.Empty(out11)
	is.Empty(out12)
	is.Empty(out13)
	is.Empty(out14)
	is.Empty(out15)
	is.Equal([]int{0}, out16)
	is.Equal([]int{0, 1, 2}, out17)
	is.Equal([]int{0, 1, 2, 3, 4}, out18)
	is.Empty(out19)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Slice(allStrings, 0, 2)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestReplace(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	in := []int{0, 1, 0, 1, 2, 3, 0}

	out1 := Replace(in, 0, 42, 2)
	out2 := Replace(in, 0, 42, 1)
	out3 := Replace(in, 0, 42, 0)
	out4 := Replace(in, 0, 42, -1)
	out5 := Replace(in, 0, 42, -1)
	out6 := Replace(in, -1, 42, 2)
	out7 := Replace(in, -1, 42, 1)
	out8 := Replace(in, -1, 42, 0)
	out9 := Replace(in, -1, 42, -1)
	out10 := Replace(in, -1, 42, -1)

	is.Equal([]int{42, 1, 42, 1, 2, 3, 0}, out1)
	is.Equal([]int{42, 1, 0, 1, 2, 3, 0}, out2)
	is.Equal([]int{0, 1, 0, 1, 2, 3, 0}, out3)
	is.Equal([]int{42, 1, 42, 1, 2, 3, 42}, out4)
	is.Equal([]int{42, 1, 42, 1, 2, 3, 42}, out5)
	is.Equal([]int{0, 1, 0, 1, 2, 3, 0}, out6)
	is.Equal([]int{0, 1, 0, 1, 2, 3, 0}, out7)
	is.Equal([]int{0, 1, 0, 1, 2, 3, 0}, out8)
	is.Equal([]int{0, 1, 0, 1, 2, 3, 0}, out9)
	is.Equal([]int{0, 1, 0, 1, 2, 3, 0}, out10)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Replace(allStrings, "0", "2", 1)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestReplaceAll(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	in := []int{0, 1, 0, 1, 2, 3, 0}

	out1 := ReplaceAll(in, 0, 42)
	out2 := ReplaceAll(in, -1, 42)

	is.Equal([]int{42, 1, 42, 1, 2, 3, 42}, out1)
	is.Equal([]int{0, 1, 0, 1, 2, 3, 0}, out2)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := ReplaceAll(allStrings, "0", "2")
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestClone(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	// Test with int slice
	original1 := []int{1, 2, 3, 4, 5}
	result1 := Clone(original1)
	is.Equal([]int{1, 2, 3, 4, 5}, result1)

	// Verify it's a different slice by checking that modifying one doesn't affect the other
	original1[0] = 99
	is.Equal([]int{99, 2, 3, 4, 5}, original1)
	is.Equal([]int{1, 2, 3, 4, 5}, result1)

	// Test with string slice
	original2 := []string{"a", "b", "c"}
	result2 := Clone(original2)
	is.Equal([]string{"a", "b", "c"}, result2)

	// Test with empty slice
	original3 := []int{}
	result3 := Clone(original3)
	is.Equal([]int{}, result3)
	is.Empty(result3)

	// Test with nil slice
	var original4 []int
	result4 := Clone(original4)
	is.Nil(result4)

	// Verify shallow copy behavior - modifying clone doesn't affect original
	original5 := []int{1, 2, 3}
	result5 := Clone(original5)
	result5[0] = 99
	is.Equal([]int{1, 2, 3}, original5) // Original unchanged
	is.Equal([]int{99, 2, 3}, result5)  // Clone changed

	type myStrings []string
	original6 := myStrings{"", "foo", "bar"}
	result6 := Clone(original6)
	result6[0] = "baz"
	is.Equal(myStrings{"", "foo", "bar"}, original6)  // Original unchanged
	is.Equal(myStrings{"baz", "foo", "bar"}, result6) // Clone changed
}

func TestCompact(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	r1 := Compact([]int{2, 0, 4, 0})

	is.Equal([]int{2, 4}, r1)

	r2 := Compact([]string{"", "foo", "", "bar", ""})

	is.Equal([]string{"foo", "bar"}, r2)

	r3 := Compact([]bool{true, false, true, false})

	is.Equal([]bool{true, true}, r3)

	type foo struct {
		bar int
		baz string
	}

	// slice of structs
	// If all fields of an element are zero values, Compact removes it.

	r4 := Compact([]foo{
		{bar: 1, baz: "a"}, // all fields are non-zero values
		{bar: 0, baz: ""},  // all fields are zero values
		{bar: 2, baz: ""},  // bar is non-zero
	})

	is.Equal([]foo{{bar: 1, baz: "a"}, {bar: 2, baz: ""}}, r4)

	// slice of pointers to structs
	// If an element is nil, Compact removes it.

	e1, e2, e3 := foo{bar: 1, baz: "a"}, foo{bar: 0, baz: ""}, foo{bar: 2, baz: ""}
	// NOTE: e2 is a zero value of foo, but its pointer &e2 is not a zero value of *foo.
	r5 := Compact([]*foo{&e1, &e2, nil, &e3})

	is.Equal([]*foo{&e1, &e2, &e3}, r5)

	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Compact(allStrings)
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestIsSorted(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.True(IsSorted([]int{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}))
	is.True(IsSorted([]string{"a", "b", "c", "d", "e", "f", "g", "h", "i", "j"}))

	is.False(IsSorted([]int{0, 1, 4, 3, 2, 5, 6, 7, 8, 9, 10}))
	is.False(IsSorted([]string{"a", "b", "d", "c", "e", "f", "g", "h", "i", "j"}))
}

func TestIsSortedBy(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	is.True(IsSortedBy([]string{"a", "bb", "ccc"}, func(s string) int {
		return len(s)
	}))

	is.False(IsSortedBy([]string{"aa", "b", "ccc"}, func(s string) int {
		return len(s)
	}))

	is.True(IsSortedBy([]string{"1", "2", "3", "11"}, func(s string) int {
		ret, _ := strconv.Atoi(s)
		return ret
	}))
}

func TestSplice(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	sample := []string{"a", "b", "c", "d", "e", "f", "g"}

	// normal case
	results := Splice(sample, 1, "1", "2")
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, sample)
	is.Equal([]string{"a", "1", "2", "b", "c", "d", "e", "f", "g"}, results)

	// check there is no side effect
	results = Splice(sample, 1)
	results[0] = "b"
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, sample)

	// positive overflow
	results = Splice(sample, 42, "1", "2")
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, sample)
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g", "1", "2"}, results)

	// negative overflow
	results = Splice(sample, -42, "1", "2")
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, sample)
	is.Equal([]string{"1", "2", "a", "b", "c", "d", "e", "f", "g"}, results)

	// backward
	results = Splice(sample, -2, "1", "2")
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, sample)
	is.Equal([]string{"a", "b", "c", "d", "e", "1", "2", "f", "g"}, results)

	results = Splice(sample, -7, "1", "2")
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, sample)
	is.Equal([]string{"1", "2", "a", "b", "c", "d", "e", "f", "g"}, results)

	// other
	is.Equal([]string{"1", "2"}, Splice([]string{}, 0, "1", "2"))
	is.Equal([]string{"1", "2"}, Splice([]string{}, 1, "1", "2"))
	is.Equal([]string{"1", "2"}, Splice([]string{}, -1, "1", "2"))
	is.Equal([]string{"1", "2", "0"}, Splice([]string{"0"}, 0, "1", "2"))
	is.Equal([]string{"0", "1", "2"}, Splice([]string{"0"}, 1, "1", "2"))
	is.Equal([]string{"1", "2", "0"}, Splice([]string{"0"}, -1, "1", "2"))

	// type preserved
	type myStrings []string
	allStrings := myStrings{"", "foo", "bar"}
	nonempty := Splice(allStrings, 1, "1", "2")
	is.IsType(nonempty, allStrings, "type preserved")
}

func TestCutSuccess(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	// case 1
	actualLeft, actualRight, result := Cut([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b"})
	is.True(result)
	is.Equal([]string{}, actualLeft)
	is.Equal([]string{"c", "d", "e", "f", "g"}, actualRight)

	// case 2
	actualLeft, actualRight, result = Cut([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"f", "g"})
	is.True(result)
	is.Equal([]string{"a", "b", "c", "d", "e"}, actualLeft)
	is.Equal([]string{}, actualRight)

	// case 3
	actualLeft, actualRight, result = Cut([]string{"g"}, []string{"g"})
	is.True(result)
	is.Equal([]string{}, actualLeft)
	is.Equal([]string{}, actualRight)

	// case 4
	actualLeft, actualRight, result = Cut([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"b", "c"})
	is.True(result)
	is.Equal([]string{"a"}, actualLeft)
	is.Equal([]string{"d", "e", "f", "g"}, actualRight)

	// case 5
	actualLeft, actualRight, result = Cut([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"e", "f"})
	is.True(result)
	is.Equal([]string{"a", "b", "c", "d"}, actualLeft)
	is.Equal([]string{"g"}, actualRight)

	// case 6
	actualLeft, actualRight, result = Cut([]string{"a", "b"}, []string{"b"})
	is.True(result)
	is.Equal([]string{"a"}, actualLeft)
	is.Equal([]string{}, actualRight)

	// case 7
	actualLeft, actualRight, result = Cut([]string{"a", "b"}, []string{"a"})
	is.True(result)
	is.Equal([]string{}, actualLeft)
	is.Equal([]string{"b"}, actualRight)
}

func TestCutFail(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	// case 1
	actualLeft, actualRight, result := Cut([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"z"})
	is.False(result)
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actualLeft)
	is.Equal([]string{}, actualRight)

	// case 2
	actualLeft, actualRight, result = Cut([]string{}, []string{"z"})
	is.False(result)
	is.Equal([]string{}, actualLeft)
	is.Equal([]string{}, actualRight)

	// case 3
	actualLeft, actualRight, result = Cut([]string{"a"}, []string{"z"})
	is.False(result)
	is.Equal([]string{"a"}, actualLeft)
	is.Equal([]string{}, actualRight)
}

type TestCutStruct struct {
	id   int
	data string
}

func TestCutPrefix(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	// case 1
	actualAfter, result := CutPrefix(
		[]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}},
		[]TestCutStruct{{id: 1, data: "a"}},
	)
	is.True(result)
	is.Equal([]TestCutStruct{{id: 2, data: "a"}, {id: 2, data: "b"}}, actualAfter)

	// case 2
	actualAfter, result = CutPrefix(
		[]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}},
		[]TestCutStruct{},
	)
	is.True(result)
	is.Equal([]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}}, actualAfter)

	// case 3
	actualAfter, result = CutPrefix(
		[]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}},
		[]TestCutStruct{{id: 2, data: "b"}},
	)
	is.False(result)
	is.Equal([]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}}, actualAfter)

	// case 4
	actualAfter, result = CutPrefix(
		[]TestCutStruct{},
		[]TestCutStruct{{id: 2, data: "b"}},
	)
	is.False(result)
	is.Equal([]TestCutStruct{}, actualAfter)

	// case 5
	actualAfterS, result := CutPrefix([]string{"a", "a", "b"}, []string{})
	is.True(result)
	is.Equal([]string{"a", "a", "b"}, actualAfterS)
}

func TestCutSuffix(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	// case 1
	actualBefore, result := CutSuffix(
		[]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}},
		[]TestCutStruct{{id: 3, data: "b"}},
	)
	is.False(result)
	is.Equal([]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}}, actualBefore)

	// case 2
	actualBefore, result = CutSuffix(
		[]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}},
		[]TestCutStruct{{id: 2, data: "b"}},
	)
	is.True(result)
	is.Equal([]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}}, actualBefore)

	// case 3
	actualBefore, result = CutSuffix(
		[]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}},
		[]TestCutStruct{},
	)
	is.True(result)
	is.Equal([]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}}, actualBefore)

	// case 4
	actualBefore, result = CutSuffix(
		[]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}},
		[]TestCutStruct{{id: 2, data: "a"}},
	)
	is.False(result)
	is.Equal([]TestCutStruct{{id: 1, data: "a"}, {id: 2, data: "a"}, {id: 2, data: "b"}}, actualBefore)

	// case 5
	actualAfterS, result := CutSuffix([]string{"a", "a", "b"}, []string{})
	is.True(result)
	is.Equal([]string{"a", "a", "b"}, actualAfterS)
}

func TestTrim(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	actual := Trim([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b"})
	is.Equal([]string{"c", "d", "e", "f", "g"}, actual)
	actual = Trim([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"g", "f"})
	is.Equal([]string{"a", "b", "c", "d", "e"}, actual)
	actual = Trim([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b", "c", "d", "e", "f", "g"})
	is.Equal([]string{}, actual)
	actual = Trim([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b", "c", "d", "e", "f", "g", "h"})
	is.Equal([]string{}, actual)
	actual = Trim([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
}

func TestTrimLeft(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	actual := TrimLeft([]string{"a", "a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b"})
	is.Equal([]string{"c", "d", "e", "f", "g"}, actual)
	actual = TrimLeft([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"b", "a"})
	is.Equal([]string{"c", "d", "e", "f", "g"}, actual)
	actual = TrimLeft([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"g", "f"})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
	actual = TrimLeft([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b", "c", "d", "e", "f", "g"})
	is.Equal([]string{}, actual)
	actual = TrimLeft([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b", "c", "d", "e", "f", "g", "h"})
	is.Equal([]string{}, actual)
	actual = TrimLeft([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
}

func TestTrimPrefix(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	actual := TrimPrefix([]string{"a", "b", "a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b"})
	is.Equal([]string{"c", "d", "e", "f", "g"}, actual)
	actual = TrimPrefix([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"b", "a"})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
	actual = TrimPrefix([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"g", "f"})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
	actual = TrimPrefix([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b", "c", "d", "e", "f", "g"})
	is.Equal([]string{}, actual)
	actual = TrimPrefix([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b", "c", "d", "e", "f", "g", "h"})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
	actual = TrimPrefix([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
}

func TestTrimRight(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	actual := TrimRight([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b"})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
	actual = TrimRight([]string{"a", "b", "c", "d", "e", "f", "g", "g"}, []string{"g", "f"})
	is.Equal([]string{"a", "b", "c", "d", "e"}, actual)
	actual = TrimRight([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b", "c", "d", "e", "f", "g"})
	is.Equal([]string{}, actual)
	actual = TrimRight([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b", "c", "d", "e", "f", "g", "h"})
	is.Equal([]string{}, actual)
	actual = TrimRight([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
}

func TestTrimSuffix(t *testing.T) {
	t.Parallel()
	is := assert.New(t)

	actual := TrimSuffix([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b"})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
	actual = TrimSuffix([]string{"a", "b", "c", "d", "e", "f", "g", "f", "g"}, []string{"f", "g"})
	is.Equal([]string{"a", "b", "c", "d", "e"}, actual)
	actual = TrimSuffix([]string{"a", "b", "c", "d", "e", "f", "g", "f", "g"}, []string{"g", "f"})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g", "f", "g"}, actual)
	actual = TrimSuffix([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b", "c", "d", "e", "f", "g"})
	is.Equal([]string{}, actual)
	actual = TrimSuffix([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{"a", "b", "c", "d", "e", "f", "g", "h"})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
	actual = TrimSuffix([]string{"a", "b", "c", "d", "e", "f", "g"}, []string{})
	is.Equal([]string{"a", "b", "c", "d", "e", "f", "g"}, actual)
}