@Test
public void testFlagFlaggedField() {

    Game game = new Game(2, 2, 2, new TestBoardMiner(new boolean[][]{{false, false}, {true, true}}));
    openAt(0, 0, game);
    IField field = flagAt(1, 1, game);
    game.onRequestFlag(field);
    assertEquals(false, field.isFlagged());
}