    @Test
    public void repeatTest() {

        assertEquals(repeat('c', -1), "");
        assertEquals(repeat('c', 3), "ccc");
        assertEquals(repeat('c', 1), "c");
        assertEquals(repeat('c', 0), "");

        assertNull(repeat(null, 1));
        assertEquals(repeat("ab", -1), "");
        assertEquals(repeat("ab", 3), "ababab");
        assertEquals(repeat("ab", 1), "ab");
        assertEquals(repeat("ab", 0), "");
    }