The normal expected functionality with logging in to the sandbox app with the wrong credentials is broken.
Test 1: Login Failure Functionality Error
It appears that the wrong credentials is letting users into the application. Try username=alice and a random password.
Test 2: Login Failure Functionality Is Broken Error
The functionality of entering the wrong credentials is different than before the code was updated. Try entering the wrong credentials with your code and with the original code and see how they differ.