private void Test(String description, PokerHand.Result expected, String playerHand, String opponentHand)
{
PokerHand player = new PokerHand(playerHand);
PokerHand opponent = new PokerHand(opponentHand);
-->PokerHand.Result r = player.compareWith(opponent);

    assertEquals(description + ":", expected.toString(), player.compareWith(opponent).toString());
}

In your example test class, and also in your second test the variable r is never used, causing the method compareWith() to be called twice.

You could either remove the line with the --> next to it or change:

assertEquals(description + ":", expected.toString(), player.compareWith(opponent).toString());

to

assertEquals(description + ":", expected.toString(), r.toString());