Added ValidateCell tests (in GameEngine tests)
        public void TestValidateCellOpenedCell()
        {
            GameEngine e

            engine.OpenCell(2, 2);
            bool actual = engine.ValidateCell(2, 2);
            bool expected = false;
            Assert.AreEqual(expected, actual, "ValidateCell method not correct checking.");
        }
[TestMethod]
        public void TestValidateCellOpenedCell()
        {
            GameEngine engine = new GameEngine(3, 5, 6);
            engine.StartNewGame();
            engine.OpenCell(2, 2);
            bool actual = engine.ValidateCell(2, 2);
            bool expected = false;
            Assert.AreEqual(expected, actual, "ValidateCell method not correct checking.");
        }