Node.js unit testing: Test behaviour when fs module throws error?

How can you test the behaviour of a module when an fs module function throws an error? I have this code:

fs.stat('/Users/' + username.sync() + '/Library/LaunchAgents/' + key + '.plist', function(error, stat) {

 if (!error) {
   callback(null, true);
 } else if (error.code == 'ENOENT') {
   callback(null, false);
 } else {
   callback(error, null);
 }

 return;
});

But currently, the else path is never run during tests. What would be the best-practise way to cover this line?

Thanks