Test testNextPieceReallyUsed

Assert.assertEquals("getNextPiece() did not predict really used piece", nextPiece, g.getCurrentPiece());

I don’t really understand what this test tests can anyone explain it to me so I can fix my wrong implementation? when using the function newPiece() I am putting the nextPiece at the given posistion and then reassigning the nextPiece.

The test is public. Have you run it under a debugger to see what precisely it does and (importantly) what your own code is doing?