Added unit tests for DotsAndBoxesGrid

src/test/java/dotsandboxes/DotsAndBoxesGridTest.java

@@ -27,5 +27,30 @@ public class DotsAndBoxesGridTest {
         assertTrue(true);
     }
 
-    // FIXME: You need to write tests for the two known bugs in the code.
+    @Test
+    public void testSquareCompletion() {
+        DotsAndBoxesGrid grid = new DotsAndBoxesGrid(3, 3, 2);
+
+        // Draw the four lines of a box
+        grid.drawHorizontal(0, 0, 1);
+        grid.drawHorizontal(0, 1, 1);
+        grid.drawVertical(0, 0, 1);
+        grid.drawVertical(1, 0, 1);
+
+        // Check if the box is indeed complete
+        assertTrue(grid.boxComplete(0, 0));
+    }
+
+    @Test
+    public void testDrawExistingLine() {
+        DotsAndBoxesGrid grid = new DotsAndBoxesGrid(3, 3, 2);
+
+        // Draw a line
+        grid.drawHorizontal(0, 0, 1);
+
+        // Attempt to draw the same line again. This should throw an IllegalStateException.
+        assertThrows(IllegalStateException.class, () -> {
+            grid.drawHorizontal(0, 0, 1);
+        });
+    }
 }