bugs fixed, gradle tests pass

src/main/java/dotsandboxes/DotsAndBoxesGrid.java

@@ -112,8 +112,14 @@ 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;
+        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. */
@@ -139,9 +145,9 @@ public class DotsAndBoxesGrid {
         if (y >= height || y < 0) {
             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] == true) {
+            throw new IllegalStateException("You cannot draw on a new line ontop of an already existing line");
+        }
         this.horizontals[x][y] = true;
 
         // Try to claim the north or south boxes
@@ -170,8 +176,9 @@ public class DotsAndBoxesGrid {
         if (y >= height - 1 || y < 0) {
             throw new IndexOutOfBoundsException(String.format("y was %d, which is out of range. Range is 0 to %d", y, height - 1));
         }
-
-        // You need to throw an exception if the line was already drawn.
+        if (this.verticals[x][y] == true) {
+            throw new IllegalStateException("You cannot draw on a new line ontop of an already existing line");
+        }
 
         this.verticals[x][y] = true;
         // Try to claim the north or south boxes