@Test
public void testWithSource() {

  assertEquals("foo", FOO.withSource().toString());
  assertEquals(new WithSource<String>("foo", ""), FOO.withSource().parse("", mode));
  assertEquals(new WithSource<Integer>(123, "123"), INTEGER.withSource().parse("123", mode));
  assertFailure(mode, INTEGER.withSource(), "a", 1, 1);
}