Fixed bugs in box completion and duplicate line drawing

src/main/java/dotsandboxes/DotsAndBoxesGrid.java

@@ -112,7 +112,9 @@ 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).
-        return true;
+            // A box is complete if the north and south horizontals and the east and west verticals have all been drawn.
+        return getHorizontal(x, y) && getHorizontal(x, y + 1) &&
+           getVertical(x, y) && getVertical(x + 1, y);
     }
 
     /** Tries to claim a box for a player. If the box is complete, sets the ownership and returns true. */
@@ -140,7 +142,9 @@ public class DotsAndBoxesGrid {
         }
 
         // FIXME: You need to throw an exception if the line was already drawn.
-
+        if (horizontals[x][y]) {
+                throw new IllegalStateException("Line already drawn");
+            }
         this.horizontals[x][y] = true;
 
         // Try to claim the north or south boxes
@@ -171,6 +175,9 @@ public class DotsAndBoxesGrid {
         }
 
         // You need to throw an exception if the line was already drawn.
+        if (verticals[x][y]) {
+                throw new IllegalStateException("Line already drawn");
+            }
             
         this.verticals[x][y] = true;
         // Try to claim the north or south boxes