assertTrue(isNotEmpty.apply("test"));
        assertTrue(isNotEmpty.apply("a"));
        assertFalse(isNotEmpty.apply(""));
        assertFalse(isNotEmpty.apply(null));
    }

    public void test_apply_integer() {
        BooleanFunction<Integer> isPositive = n -> n != null && n > 0;

        assertTrue(isPositive.apply(1));
        assertTrue(isPositive.apply(100));
        assertFalse(isPositive.apply(0));