Fix bugs in code

 - Changed boxComplete method to return a bool indicating if all cardinal directions have lines drawn
 - Changed drawVertical and drawHorizontal to check the (x,y) coordinates to see if a line has already been drawn, and throws if true

src/main/java/dotsandboxes/DotsAndBoxesGrid.java

 package dotsandboxes;
 
-
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.function.Consumer;
@@ -50,6 +49,7 @@ public class DotsAndBoxesGrid {
 
   final int players;
   private int player = 1;
+
   public int getPlayer() {
     return player;
   }
@@ -98,7 +98,6 @@ public class DotsAndBoxesGrid {
     return boxOwners[x][y];
   }
 
-
   /**
    * Checks whether a box has been fully drawn (all four sides)
    * @param x coordinate of the left side of the box
@@ -111,10 +110,18 @@ 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 (
+      getHorizontal(x, y) &&
+      getVertical(x, y) &&
+      getHorizontal(x, y + 1) &&
+      getVertical(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. */
   private boolean claimBox(int x, int y, int p) {
     if (boxComplete(x, y)) {
@@ -133,13 +140,33 @@ public class DotsAndBoxesGrid {
    */
   public boolean drawHorizontal(int x, int y, int player) {
     if (x >= width - 1 || x < 0) {
-            throw new IndexOutOfBoundsException(String.format("x was %d, which is out of range. Range is 0 to %d", x, width - 1));
+      throw new IndexOutOfBoundsException(
+        String.format(
+          "x was %d, which is out of range. Range is 0 to %d",
+          x,
+          width - 1
+        )
+      );
     }
     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));
+      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 (getHorizontal(x, y)) {
+      throw new RuntimeException(
+        String.format(
+          "Error: Horizontal line has already been drawn at (%d,%d).",
+          x,
+          y
+        )
+      );
+    }
 
     this.horizontals[x][y] = true;
 
@@ -164,13 +191,33 @@ public class DotsAndBoxesGrid {
    */
   public boolean drawVertical(int x, int y, int player) {
     if (x >= width || x < 0) {
-            throw new IndexOutOfBoundsException(String.format("x was %d, which is out of range. Range is 0 to %d", x, width));
+      throw new IndexOutOfBoundsException(
+        String.format(
+          "x was %d, which is out of range. Range is 0 to %d",
+          x,
+          width
+        )
+      );
     }
     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));
+      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 (getVertical(x, y)) {
+      throw new RuntimeException(
+        String.format(
+          "Error: Vertical line has already been drawn at (%d,%d).",
+          x,
+          y
+        )
+      );
+    }
 
     this.verticals[x][y] = true;
     // Try to claim the north or south boxes
@@ -184,14 +231,13 @@ public class DotsAndBoxesGrid {
       notifyObservers();
       return false;
     }
-
   }
 
   public boolean gameComplete() {
     // Students who took COSC250 might recognise this style of code. This is Java's version of higher order functions.
     // The grid is complete if "for all rows, all the boxes in that row have a non-zero owner"
-        return Arrays.stream(boxOwners).allMatch((row) -> Arrays.stream(row).allMatch((owner) -> owner > 0));
+    return Arrays
+      .stream(boxOwners)
+      .allMatch(row -> Arrays.stream(row).allMatch(owner -> owner > 0));
   }
-
-
 }