Add assertActivePlayer test method.

Mage.Tests/src/test/java/org/mage/test/serverside/base/impl/CardTestPlayerAPIImpl.java

@@ -917,6 +917,10 @@ public abstract class CardTestPlayerAPIImpl extends MageTestPlayerBase implement
         Assert.assertEquals("Actions left are not equal: ", count, player.getActionCount());
     }
 
+    public void assertActivePlayer(TestPlayer player) {
+        Assert.assertEquals("message", currentGame.getState().getActivePlayerId(), player.getId());
+    }
+
     public Permanent getPermanent(String cardName, Player player) {
         return getPermanent(cardName, player.getId());
     }