src/main/java/dotsandboxes/DotsAndBoxesGrid.java

@@ -112,8 +112,13 @@ public class DotsAndBoxesGrid {
 
         // A box is complete if the north and south horizontals and the east and west verticals have all been drawn.
         // FIXME: You'll need to fix this code (after writing a test first).
+        if (getHorizontal(0, 0) && getHorizontal(0, 1) && getVertical(0, 0) && getVertical(1, 0)) {
             return true;
         }
+        else
+            return false;
+    }
+
 
     /** Tries to claim a box for a player. If the box is complete, sets the ownership and returns true. */
     private boolean claimBox(int x, int y, int p) {
@@ -140,6 +145,7 @@ public class DotsAndBoxesGrid {
         }
 
         // FIXME: You need to throw an exception if the line was already drawn.
+        if (getHorizontal(x, y)) throw new IllegalStateException();
 
         this.horizontals[x][y] = true;
 

src/test/java/dotsandboxes/DotsAndBoxesGridTest.java

@@ -28,4 +28,26 @@ public class DotsAndBoxesGridTest {
     }
 
     // FIXME: You need to write tests for the two known bugs in the code.
+
+    /* Test a grid with lines forming a complete box */
+    @Test
+    public void testIfBoxComplete() {
+        logger.info("test a grid with lines forming a complete box");
+        DotsAndBoxesGrid grid = new DotsAndBoxesGrid(4, 3, 1);
+        assertFalse(grid.boxComplete(0, 0));
+
+    }
+
+    /* Test if drawing a duplicate line throws IllegalStateException */
+    @Test
+    public void testDrawDuplicateLine() {
+        logger.info("Test if drawing a duplicate line throws IllegalStateException");
+        DotsAndBoxesGrid grid = new DotsAndBoxesGrid(5, 3, 2);
+        grid.drawHorizontal(1, 1, 1);
+
+        assertThrows(IllegalStateException.class, () -> {
+            grid.drawHorizontal(1, 1, 1);
+        });
+    }
+
 }