a.Insert("")
	if !a.Equal(b) {
		t.Errorf("Expected to be equal: %v vs %v", a, b)
	}

	a.Delete("")
	if a.Equal(b) {
		t.Errorf("Expected to be not-equal: %v vs %v", a, b)
	}
}

func TestStringUnion(t *testing.T) {
	tests := []struct {
		s1       String
		s2       String
		expected String
	}{
		{
			NewString("1", "2", "3", "4"),
			NewString("3", "4", "5", "6"),