Test – occupied spot

Now that we know that pieces are placed within the board's boundaries, we should make sure that they can be placed only on unoccupied spaces:

@Test 
public void whenOccupiedThenRuntimeException() { 
  ticTacToe.play(2, 1); 
  exception.expect(RuntimeException.class); 
  ticTacToe.play(2, 1); 
} 

That's it; this was our last test. Once the implementation is finished, we can consider the first requirement as done.