FlatMap function for arrays/slices in Go

How to write a functional FlatMap function in golang using generics, including a unit test. Basically map and flatten in one go!

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FlatMap applies a function to each element in the input slice and returns a new slice with the results concatenated. The function f takes an element of type A and returns a slice of elements of type B.

func FlatMap[A, B any](input []A, f func(A) []B) []B {
	var result []B
	for _, v := range input {
		result = append(result, f(v)...)
	}
	return result
}

and this is a unittest for the function:

func TestFlatMap(t *testing.T) {
	input := []int{1, 2, 3}
	f := func(a int) []int {
		return []int{a, a * 2}
	}
	expected := []int{1, 2, 2, 4, 3, 6}
	result := util.FlatMap(input, f)
	if !reflect.DeepEqual(expected, result) {
		t.Errorf("Expected %v, got %v", expected, result)
	}
}