This merge merges issue branch into main branch. For my project, the issue
branch contains the bugfixes in the DotsAndBoxesGrid.java class and the main
branch contains testing code.

Fixed the bug in drawHorizontal and drawVertical method. Which was to write code that would throw an exception when the user tries to draw a line on top of an existing line.

Fixed the code in the boxComplete method, which was to check north and south horizontal lines and east and west vertical lines in-order to determine if the box is complete or not.

Added two more test methods that tests if drawing a horizontal line or vertical line on top of another would throw an IllegalArgumentException error. Both test methods failed.

Added a test to check whether the game completes a box upon adding just one horizontal line. The test fails.

This switches to just using Swing and no modules for better compatibility with working with VS Code.

0.0.10 seems to have fixed the issue with running modular JavaFX
  projects, allowing us to drop the previous (manual) fix.