@Test( expected = IllegalArgumentException.class )
public void testMergeSignatures_withDifferentPubKeys() throws Exception
{

    PGPPublicKey alicePuKey = PGPTestDataFactory.getPublicKey( "alice" );
    PGPPublicKey applePubKey = PGPTestDataFactory.getPublicKey( "apple" );
    PGPSignatureUtil.mergeSignatures( alicePuKey, applePubKey );
}