src/main/java/dotsandboxes/DotsAndBoxesGrid.java

@@ -112,6 +112,10 @@ 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+1][y] || !verticals[x][y] || !verticals[x][y+1]){
+            return false;
+        }
+
         return true;
     }
 
@@ -140,6 +144,9 @@ public class DotsAndBoxesGrid {
         }
 
         // FIXME: You need to throw an exception if the line was already drawn.
+        if(horizontals[x][y]){
+            throw new IllegalStateException("Line already drawn");
+        }
 
         this.horizontals[x][y] = true;
 
@@ -171,6 +178,9 @@ public class DotsAndBoxesGrid {
         }
 
         // You need to throw an exception if the line was already drawn.
+        if(verticals[x][y]){
+            throw new IllegalStateException("Line already drawn");
+        }
 
         this.verticals[x][y] = true;
         // Try to claim the north or south boxes