Flatten integers

flatten.go

package utils

// FlattenIntegers flattens nested slices of integers
func FlattenIntegers(slice []interface{}) []int {
	var flat []int

	for _, element := range slice {
		switch element.(type) {
		case []interface{}:
			flat = append(flat, FlattenIntegers(element.([]interface{}))...)
		case []int:
			flat = append(flat, element.([]int)...)
		case int:
			flat = append(flat, element.(int))
		}
	}

	return flat
}

flatten_test.go

package utils

import (
	"fmt"
	"testing"

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

func TestFlattenIntegers(t *testing.T) {
	testCases := []struct {
		description string
		input       []interface{}

		expectedOutput []int
	}{
		{
			description: "Input contains only integers",
			input: []interface{}{
				1,
				2,
				3,
				4,
				5,
			},
			expectedOutput: []int{1, 2, 3, 4, 5},
		},
		{
			description: "Input contains only slices of integers",
			input: []interface{}{
				[]int{
					1,
				},
				[]int{
					2,
				},
				[]int{
					3,
				},
				[]int{
					4,
				},
				[]int{
					5,
				},
			},
			expectedOutput: []int{1, 2, 3, 4, 5},
		},
		{
			description: "Input contains only nested slices of integers",
			input: []interface{}{
				[]interface{}{
					[]interface{}{
						[]int{
							1,
						},
					},
				},
				[]interface{}{
					[]interface{}{
						[]int{
							2,
						},
					},
				},
				[]interface{}{
					[]interface{}{
						[]int{
							3,
						},
					},
				},
			},
			expectedOutput: []int{1, 2, 3},
		},
		{
			description: "Input contains only invalid types",
			input: []interface{}{
				"not a number",
				[]interface{}{
					[]interface{}{
						"not a number",
					},
				},
			},
			expectedOutput: []int(nil),
		},
		{
			description: "Input contains a mix of all possible cases",
			input: []interface{}{
				1,
				[]int{
					2,
					3,
				},
				[]interface{}{
					[]int{
						4,
						5,
					},
				},
				"not a number",
				[]interface{}{
					[]interface{}{
						"not a number",
					},
				},
			},
			expectedOutput: []int{1, 2, 3, 4, 5},
		},
	}
	for index, testCase := range testCases {
		assert.Equal(t, testCase.expectedOutput, FlattenIntegers(testCase.input), fmt.Sprintf("unexpected output for test %d", index))
	}
}