- Validate user input to make sure user enters l, d, t, or d to tilt board, or x to exit.
- Add signature of tiltLeft, tiltRight, tiltTop, and tiltDown methods in Board class
- Call appropriate method in Run class based on user input.
- Add score variable in Board class, and implement setter and getter methods to it.
-Display game over message and user score in case game is over or user entered 'x' to exit.
-Add getRandomNumberBetween0And3() method in Board class to return random number between 0 and 3.
-Add getRandomNumber2Or4 method in Board class, to randomly return 2 or 4
-add populateRandomCell method in Board class, to randomly populate a free tile with 2 or 4.
- Update Board class, call populaterandomCell method towice in the constructor to initiate board with 2 random cells.
- update Board class, implement tiltLeft method, to tilt board to left direction.
- Update Board class, implement tiltRight method, to tilt board to right direction.
- Update Board class, implement tiltTop method, to tilt board to top direction.
- Update Board class, implement tiltDown method, to tilt board to down direction.
- Add getter and setter to tiles array in board class
- Add import statement to Test class
- Add Test class, and implement testTiltRight() method to test tiltRight method in Board class.
-  Add Test class, and implement testTiltTop() method to test tiltTop method in Board class.
- Add Test class, and implement testTiltDown() method to test tiltDown method in Board class.