help me fix my logic mistake in JAVA

In the following JAVA class I had to implement a few methods

import java.util.$*$;

$/**$

$*$ Class that represents a maze with N$*$N junctions.

$*$

$*/$

public class Maze$\{$

private final int N;

private Graph M; $//$Maze

public int startnode;

public Maze$($int N$,$ int startnode$)\{$

if $($N $<0)$ throw new IllegalArgumentException$("$Number of vertices in a row must be nonnegative"$)$;

this.N $=$ N;

this.M$=$ new Graph$($N$*$N$)$;

this.startnode$=$ startnode;

buildMaze$()$;

$\}$

public Maze $($In in$)\{$

this.M $=$ new Graph$($in$)$;

this.N$=($int$)$ Math.sqrt$($M$.$V$())$;

this.startnode$=0$;

$\}$

private void validateVertex$($int v$)\{$

#implemented

int V $=$ M$.$V$()$;

if $($v $<0||$ v $>=$ V$)$

throw new IllegalArgumentException$("$vertex $"+$ v $+"$ is not between $0$ and $"+($V $-1))$;

$\}$

$/**$

$*$ Adds the undirected edge v$-$w to the graph M$.$

$*$

$*$ @param v one vertex in the edge

$*$ @param w the other vertex in the edge

$*$ @throws IllegalArgumentException unless both $\{$@code $0<=$ v $<$ V$\}$ and $\{$@code $0<=$ w $<$ V$\}$

$*/$

public void addEdge$($int v$,$ int w$)\{$

#implemented

validateVertex$($v$)$;

validateVertex$($w$)$;

if $(!$hasEdge$($v$,$ w$)$ && v $!=$ w$)\{$

M$.$addEdge$($v$,$ w$)$;

$\}$

$\}$

$/**$

$*$ Returns true if there is an edge between $\text{'}$v$\text{'}$ and $\text{'}$w$\text{'}$

$*$ @param v one vertex

$*$ @param w another vertex

$*$ @return true or false

$*/$

public boolean hasEdge$($ int v$,$ int w$)\{$

#implemented

if $($v $<0||$ v $>=$ M$.$V$()||$ w $<0||$ w $>=$ M$.$V$())\{$

return false;

$\}$

if $($v $==$ w$)\{$

return true;

$\}$

return M$.$adj$($v$).$contains$($w$)$;

$\}$

$/**$

$*$ Builds a grid as a graph.

$*$ @return Graph G $--$ Basic grid on which the Maze is built

$*/$

public Graph mazegrid$()\{$

#implemented

Graph g $=$ new Graph$($N $*$ N$)$;

for $($int y $=0$; y $<$ N; y$++)\{$

for $($int x $=0$; x $<$ N; x$++)\{$

int current $=$ x $+$ y $*$ N;

if $($x $<$ N $-1)\{$

int right $=$ current $+1$;

g$.$addEdge$($current$,$ right$)$;

$\}$

if $($y $<$ N $-1)\{$

int down $=$ current $+$ N;

g$.$addEdge$($current$,$ down$)$;

$\}$

$\}$

$\}$

return g;

$\}$

$/**$

$*$ Builds a random maze as a graph.

$*$ The maze is build with a randomized DFS as the Graph M$.$

$*/$

private void buildMaze$()\{$

#implemented

Graph grid $=$ mazegrid$()$;

RandomDepthFirstPaths rdfs $=$ new RandomDepthFirstPaths$($grid$,$ startnode$)$;

rdfs$.$randomDFS$($grid$)$;

Set addedEdges $=$ new HashSet$<>()$;

for $($int v $=0$; v $<$ grid.V$()$; v$++)\{$

for $($int w : grid.adj$($v$))\{$

if $($rdfs$.$hasPathTo$($w$)$ && v$!=$ w$)\{$

int edgeHash $=$ Math.abs$($Math$.$min$($v$,$ w$)-$ Math.max$($v$,$ w$))*$ grid.V$()+$ Math.max$($v$,$ w$)$;

if $(!$addedEdges.contains$($edgeHash$))\{$

addEdge$($v$,$ w$)$;

addedEdges.add$($edgeHash$)$;

$\}$

$\}$

$\}$

$\}$

$\}$

$/**$

$*$ Find a path from node v to w

$*$ @param v start node

$*$ @param w end node

$*$ @return List $--$ a list of nodes on the path from v to w $($both included$)$ in the right order.

$*/$

public List findWay$($int v$,$ int w$)\{$

#implemented

RandomDepthFirstPaths rdfs $=$ new RandomDepthFirstPaths$($M$,$ v$)$;

rdfs$.$randomDFS$($M$)$;

return rdfs$.$pathTo$($w$)$;

$\}$

$/**$

$*$ @return Graph M

$*/$

public Graph M$()\{$

return M;

$\}$

public static void main$($String$[]$ args$)\{$

$//$ FOR TESTING

$\}$

$\}$

I got a few jUnit tests given and I have an error with only one

@Test

void testBuildMazeRightEdgeCount$()$ throws InvocationTargetException, NoSuchMethodException, IllegalAccessException, InterruptedException $\{$

for $($int i $=0$; i $<10$; i$++)\{//$ since the maze is random better check it more than once

for $($int size $=2$; size $<10$; size$++)\{$

int startnode $=$ ThreadLocalRandom.current$().$nextInt$(0,$ size $*$ size $-1)$;

MazeExt m $=$ new MazeExt$($size$,$ startnode$)$;

int edgesInMaze $=$ m$.$getGraphPublic$().$E$()$;

assertEquals$($size $*$ size $-1,$ edgesInMaze$)$;

$\}$

$\}$

$\}$

the error message:

org.opentest$4$j$.$AssertionFailedError:

Expected :$3$

Actual :$4$

I$\text{'}$m certain the error is a logic mistake in the private void buildMaze$()$ method, though I can't figure it out