Filter function for arrays/slices in Go

How to write a functional Filter function in Go using generics, including a unit test. A taste of functional code.

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Filter applies a predicate function to each element in the input slice and returns a new slice with the elements for which the function returns true. The function f takes an element of type A and returns a boolean.

func Filter[A any](input []A, f func(A) bool) []A {
	var result []A
	for _, v := range input {
		if f(v) {
			result = append(result, v)
		}
	}
	return result
}

and this is a unittest for the function:

func TestFilter(t *testing.T) {
	input := []int{1, 2, 3, 4, 5}
	f := func(a int) bool {
		return a%2 == 0
	}
	expected := []int{2, 4}
	result := util.Filter(input, f)
	if !reflect.DeepEqual(expected, result) {
		t.Errorf("Expected %v, got %v", expected, result)
	}
}