assertTrue(identity.apply(true));
        assertFalse(identity.apply(false));
        assertFalse(identity.apply(null));
    }

    public void test_lambda_expression() {
        BooleanFunction<String> startsWithHello = s -> s != null && s.startsWith("hello");

        assertTrue(startsWithHello.apply("hello world"));
        assertTrue(startsWithHello.apply("hello"));