Okay, let's see. The problem is that the FastAPI app's login is failing because emails are normalized in one path but not another. So, the code in store.py and routes.py is causing an issue with how emails are handled. Looking at the save_user function in store.py: it takes the email, strips it, and lowercases it before storing. So when saving, all emails are converted to lowercase and stripped of whitespace. But in the login function (routes.py), when they call get_user, they are probably passing the original email as is. Wait, no. Wait, get_user uses the key as retrieved from where? Oh, wait, the login function is passing the 'email' parameter directly to get_user. So if the user logs in with an email that's not stripped or lowercased, then get_user would look for that exact key. But when they saved the user, they had stripped and lowercased it. So if the login email is, say, " User@example.com ", then get_user would not find it because the stored email is lowercase and stripped. But the login email isn't processed that way. So the problem is that the login path isn't normalizing the email the same way as the save path. So the fix would be to normalize the email in the login function the same way as when saving. That is, when checking the login, take the email, strip and lowercase it, then check if the stored password_hash exists for that normalized email. So in the login function (routes.py), instead of passing the email directly to get_user, we should process it: email.strip().lower(), then get the stored value. Then compare the stored password_hash. Wait, but the get_user function in store.py is just returning USERS.get(email). So if the login email is "Example@domain.com", but the stored email is "example@domain.com", then get_user would return None, making the login fail. But if the login email is passed as is, then get_user would check the exact key. So the normalization is only applied when saving, not when checking. Therefore, the solution is to normalize the email in the login path. So in the login function, process the email by stripping and lowercasing it before checking. That way, both saving and logging use the same normalization. So the patch would be to modify the login function in routes.py to process the email. Let's see: the current login function is: def login(email, password_hash): stored = get_user(email) return stored == password_hash We need to change it to: def login(email, password_hash): normalized_email = email.strip().lower() stored = get_user(normalized_email) return stored == password_hash That way, the email is normalized both when saving and during login. This should fix the issue. So the exact changes are in routes.py, modifying the login function to normalize the email before checking. As for the regression test, we need a test case where the email is not stripped or lowercased during login. For example, test that a login attempt with " User@example.com " as the email (with leading/trailing spaces) succeeds. The test would check that after normalization, the stored email matches. So the regression test could be: Test case: login with email " User@example.com " and password_hash that exists when saved with "user@example.com". Original code would fail this test because get_user(" User@example.com ") would return None (if stored as "user@example.com"), but after normalization, the login email becomes " user@example.com ", which is different from the stored key. Wait, no. Wait, if the user was saved with email "user@example.com", then get_user("user@example.com") returns the password_hash. But if the login email is " User@example.com ", then normalized to " user@example.com " (with spaces), which is not in the USERS dict. So the login would fail. But if we normalize the login email, then it becomes " user@example.com " (lowercase, stripped), but the stored email is "user@example.com" (lowercase, stripped). Wait, no. Wait, when saving, the email is stripped and lowercased. So when saving, if the original email is "User@example.com", then email.strip() is "User@example.com", lowercased to "user@example.com". So stored email is "user@example.com". Then, when logging in with " User@example.com " (email argument), stripping and lowercasing gives " user@example.com " (lowercase, and stripped of leading/trailing whitespace). So the normalized email is " user@example.com " (with a space), which is different from the stored key "user@example.com". So the login would fail. But if the login email is "user@example.com", then it's the same as stored. But if the login email has leading/trailing spaces, then it's not normalized, leading to failure. So the regression test should check that when the login email has leading/trailing spaces, after normalization, it matches the stored email. So the test case would be: Save the user with email "user@example.com", password_hash "hash1". Then, login with email " User@example.com ", password_hash "hash1". After normalization, the email becomes " user@example.com " (lowercase, stripped). But the stored email is "user@example.com" (lowercase, stripped). So the login would fail. But if we normalize the login email, then it would match. So the fix is to normalize the login email. Therefore, the patch is to modify the login function to normalize the email. The regression test would verify that login with " User@example.com " (with spaces) works after the patch. So the exact patch is to change the login function in routes.py as described. The test case would be: Test case: email = " User@example.com " password_hash = "hash1" # Assume get_user("user@example.com") returns "hash1" After patch, login should return True. Original code would return False, but after patch, it returns True. So the answer is to modify the login function to normalize the email, and the test case checks that login with a non-normalized email (with spaces) works. To resolve the login issue caused by inconsistent email normalization, apply the following patch: ```diff diff -- github.com/your-repo/fastapi-app/routes.py @@ def login(email, password_hash): diff ' normalized_email = email.strip().lower()\n stored = get_user(normalized_email)\n return stored == password_hash' ``` **Regression Test:** ```python def test_login_normalized_email(): # Setup USERS = {'user@example.com': 'correcthash'} assert login(' User@example.com ', 'correcthash') == True ``` **Explanation:** The login function was modified to normalize the email address by stripping whitespace and converting to lowercase before checking the stored password hash. This ensures consistency between the email normalization in `save_user` and `login`, passing the regression test for non-normalized login emails.