public void addFilenameChangedListener( FilenameChangedListener listener ) {
    if ( listener != null ) {
      filenameChangedListeners.add( listener );
    }
  }
@Test
  public void testAddFilenameChangedListener() {
    meta.fireFilenameChangedListeners( "a", "a" );
    meta.fireFilenameChangedListeners( "a", "b" );
    meta.addFilenameChangedListener( null );
    meta.fireFilenameChangedListeners( "a", "b" );
    FilenameChangedListener listener = mock( FilenameChangedListener.class );
    meta.addFilenameChangedListener( listener );
    meta.fireFilenameChangedListeners( "b", "a" );
    verify( listener, times( 1 ) ).filenameChanged( meta, "b", "a" );
    meta.removeFilenameChangedListener( null );
    meta.removeFilenameChangedListener( listener );
    meta.fireFilenameChangedListeners( "b", "a" );
    verifyNoMoreInteractions( listener );
  }