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); }
When a piece is placed on an occupied space, then RuntimeException is thrown.
That's it; this was our last test. Once the implementation is finished, we can consider the first requirement as done.