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.