Added two more test methods that tests if drawing a horizontal line or...

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.

src/test/java/dotsandboxes/DotsAndBoxesGridTest.java

@@ -38,4 +38,30 @@ public class DotsAndBoxesGridTest {
         grid.drawHorizontal(0, 0, 1);
         assertEquals(false, grid.boxComplete(0, 0));
     }
+
+    /** This test method tests if the drawHorizontal method in DotsAndBoxesGrid.java class returns an
+     * IllegalArgumentException error when the user tries to draw a horizontal line on top of another
+     * (on top of an existing line). */
+    @DisplayName("Fails to throw an exception when attempting to draw a horizontal line on top of another")
+    @Test
+    public void testRedrawingTheLineHoriz() {
+        DotsAndBoxesGrid grid = new DotsAndBoxesGrid(4, 3, 2);
+        grid.drawHorizontal(1, 1, 1);
+        assertThrows(IllegalArgumentException.class, () -> {
+            grid.drawHorizontal(1, 1, 1);
+        });
+    }
+
+    /** This tests if the drawVertical method in DotsAndBoxesGrid.java class returns an
+     * IllegalArgumentException error when the user tries to draw a vertical line on top
+     * of another. */
+    @DisplayName("Fails to throw an exception when attempting to draw a Vertical line on top of another")
+    @Test
+    public void testRedrawingTheLineVerti() {
+        DotsAndBoxesGrid grid = new DotsAndBoxesGrid(4, 3, 2);
+        grid.drawVertical(0, 1, 1);
+        assertThrows(IllegalArgumentException.class, () -> {
+            grid.drawVertical(0, 1, 1);
+        });
+    }
 }