make a compareString function for goada_test.go

[mertcanaltin]

@lemire @anonrig hi add helper functions to prevent this code repetition? For example, if I create a helper function called compareString like

this:

func compareString(t *testing.T, expected, actual, message string) {
	if expected != actual {
		t.Errorf("Expected %s, but got %s. %s", expected, actual, message)
	}
}

[lemire]

That would be fine. PR invited.

[mertcanaltin]

That would be fine. PR invited.

ı created it here : pr