assertFalse(startsWithHello.apply("hi world"));
        assertFalse(startsWithHello.apply(""));
        assertFalse(startsWithHello.apply(null));
    }

    @Test
    public void test_method_reference() {
        BooleanFunction<String> isEmpty = String::isEmpty;

        assertTrue(isEmpty.apply(""));
        assertFalse(isEmpty.apply("test"));
        assertFalse(isEmpty.apply("a"));
    }