Fix square completion and already drawn line bugs

src/main/java/dotsandboxes/DotsAndBoxesGrid.java

@@ -112,7 +112,8 @@ 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;
+        // Check if all four sides of the box are drawn
+        return verticals[x][y] && verticals[x + 1][y] && horizontals[x][y] && horizontals[x][y + 1];
     }
 
     /** Tries to claim a box for a player. If the box is complete, sets the ownership and returns true. */
@@ -138,8 +139,10 @@ 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 (horizontals[x][y]) {
+            throw new IllegalStateException("Horizontal line already drawn.");
+        }
 
         this.horizontals[x][y] = true;
 
@@ -169,8 +172,10 @@ 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.
+        // FIXME: You need to throw an exception if the line was already drawn.
+        if (verticals[x][y]) {
+            throw new IllegalStateException("Vertical line already drawn.");
+        }
 
         this.verticals[x][y] = true;
         // Try to claim the north or south boxes