Issue 1 bugs fixed in code. Tests passed.

src/main/java/dotsandboxes/DotsAndBoxesGrid.java

@@ -113,7 +113,7 @@ 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;
+        return this.horizontals[x][y] && this.horizontals[x + 1][y] && this.verticals[x][y] && this.verticals[x][y + 1];
     }
 
     /** Tries to claim a box for a player. If the box is complete, sets the ownership and returns true. */
@@ -140,7 +140,10 @@ public class DotsAndBoxesGrid {
             throw new IndexOutOfBoundsException(String.format("y was %d, which is out of range. Range is 0 to %d", y, height));
         }
 
-        // FIXME: You need to throw an exception if the line was already drawn.
+        if(this.horizontals[x][y])
+        {
+            throw new IllegalArgumentException(String.format("Line already drawn at %d, %d", x, y));
+        }
 
         this.horizontals[x][y] = true;
 
@@ -172,7 +175,10 @@ public class DotsAndBoxesGrid {
         }
 
         // You need to throw an exception if the line was already drawn.
-
+        if(this.verticals[x][y])
+        {
+            throw new IllegalArgumentException(String.format("Line already drawn at %d, %d", x, y));
+        }
         this.verticals[x][y] = true;
         // Try to claim the north or south boxes
         boolean claimE = claimBox(x, y, player);