// Throws exception if not working correctly
    HostSpecifier unused = HostSpecifier.fromValid(spec);
    unused = HostSpecifier.from(spec);
    assertTrue(HostSpecifier.isValid(spec));
  }

  private void assertBad(String spec) {
    try {
      HostSpecifier.fromValid(spec);
      fail("Should have thrown IllegalArgumentException: " + spec);
    } catch (IllegalArgumentException expected) {
    }