Fixed code bugs - unit tests now pass

src/main/java/dotsandboxes/DotsAndBoxesGrid.java

@@ -113,8 +113,11 @@ 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(horizontals[x][y] && horizontals[x][y+1] && verticals[x][y] && verticals[x+1][y]){
             return true;
         }
+        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) {
@@ -141,6 +144,10 @@ public class DotsAndBoxesGrid {
         }
 
         // FIXME: You need to throw an exception if the line was already drawn.
+        if(this.horizontals[x][y])
+        {
+            throw new IllegalStateException(String.format("horizontal [%d,%d] has already been drawn.",x,y));
+        }
 
         this.horizontals[x][y] = true;
 
@@ -172,6 +179,10 @@ public class DotsAndBoxesGrid {
         }
 
         // You need to throw an exception if the line was already drawn.
+        if(this.verticals[x][y])
+        {
+            throw new IllegalStateException(String.format("vertical [%d,%d] has already been drawn.",x,y));
+        }
 
         this.verticals[x][y] = true;
         // Try to claim the north or south boxes