public Containerizer withAdditionalTag(String tag) {
    Preconditions.checkArgument(ImageReference.isValidTag(tag), "invalid tag '%s'", tag);
    additionalTags.add(tag);
    return this;
  }
@Test
  public void testWithAdditionalTag() throws InvalidImageReferenceException {
    Containerizer containerizer = Containerizer.to(DockerDaemonImage.named("image"));

    containerizer.withAdditionalTag("tag");
    try {
      containerizer.withAdditionalTag("+invalid+");
      Assert.fail();
    } catch (IllegalArgumentException ex) {
      Assert.assertEquals("invalid tag '+invalid+'", ex.getMessage());
    }
  }