@Override
  public int compareTo(Source other) {
    return mType.compareTo(other.mType);
  }
@Test
  public void compareTo() {
    assertEquals(-1, Source.UNKNOWN.compareTo(Source.DEFAULT));
    assertEquals(-1, Source.DEFAULT.compareTo(Source.CLUSTER_DEFAULT));
    assertEquals(-1, Source.CLUSTER_DEFAULT.compareTo(Source.REFERENCE));
    assertEquals(-1, Source.REFERENCE.compareTo(Source.siteProperty("")));
    assertEquals(-1, Source.Type.SITE_PROPERTY.compareTo(Source.Type.SYSTEM_PROPERTY));
    assertEquals(-1, Source.Type.SYSTEM_PROPERTY.compareTo(Source.Type.PATH_DEFAULT));
    assertEquals(-1, Source.PATH_DEFAULT.compareTo(Source.RUNTIME));
    assertEquals(-1, Source.RUNTIME.compareTo(Source.MOUNT_OPTION));
  }