Resolved known bugs in assignment, all unit tests now pass

src/main/java/dotsandboxes/DotsAndBoxesGrid.java

@@ -110,11 +110,14 @@ public class DotsAndBoxesGrid {
         if (x >= width - 1 || x < 0 || y >= height - 1 || y < 0) {
             return false;
         } 
-
-        // 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).
+        else if (this.getVertical(x, y) && this.getHorizontal(x, y) && this.getVertical(x + 1, y) &&
+                this.getHorizontal(x, y + 1)) {
             return true;
         }
+        else {
+            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) {
@@ -139,8 +142,9 @@ 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]) {
+            throw new IllegalStateException("This location already has a horizontal line");
+        }
 
         this.horizontals[x][y] = true;
 
@@ -171,7 +175,9 @@ public class DotsAndBoxesGrid {
             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]) {
+            throw new IllegalStateException("This location already has a vertical line");
+        }
 
         this.verticals[x][y] = true;
         // Try to claim the north or south boxes