@Test
public void testAsString() {

    assertEquals("1", Filters.asString(ff.literal("1")));
    assertEquals("1", Filters.asString(ff.literal(1)));
    assertEquals("1.0", Filters.asString(ff.literal(1.0)));
    assertEquals("3.14", Filters.asString(ff.literal(3.14)));
    assertEquals("#000000", Filters.asString(ff.literal(Color.BLACK)));
}