Added unit tests for 2 errors

src/test/java/dotsandboxes/DotsAndBoxesGridTest.java

@@ -28,4 +28,23 @@ public class DotsAndBoxesGridTest {
     }
 
     // FIXME: You need to write tests for the two known bugs in the code.
+    @Test
+    public void testCompleteBox() {
+        DotsAndBoxesGrid grid = new DotsAndBoxesGrid(15, 8, 2);
+        grid.drawHorizontal(0,0,1);
+        grid.drawVertical(0,0,1);
+        grid.drawHorizontal(0,1,1);
+        assertTrue(grid.drawVertical(1,0,1));
+    }
+
+    @Test
+    public void testLineDrawn() {
+        DotsAndBoxesGrid grid = new DotsAndBoxesGrid(15, 8, 2);
+        grid.drawHorizontal(1,1,1);
+        Throwable exception = assertThrows(IllegalStateException.class, () -> grid.drawHorizontal(1,1,1));
+        assertEquals("This line has already been drawn.", exception.getMessage());
+        grid.drawVertical(1,1,1);
+        Throwable exception2 = assertThrows(IllegalStateException.class, () -> grid.drawVertical(1,1,1));
+        assertEquals("This line has already been drawn.", exception2.getMessage());
+    }
 }