Solution for the parallel execution of tests that verify email

Question

I have a test, that reads Auth Code from mailbox and uses it to log in. I use Gmail API for that.

I would like to have several such tests, that will run in parallel.

However, I don't know, how to distinguish emails from each other, because the only thing, that is different about 2 emails is this Auth Code.

So, race condition looks like this:

1. test-1 sends an email at 00:00:00
2. test-2 sends an email at 00:00:01
3. it takes 3 seconds for the email-1 to arrive => 00:00:03,
4. it takes only 1 second for the email-2 to arrive => 00:00:02
5. test-1 reads the first unread matching email, and it is an email-2

Result: Auth code is wrong.

So, my question here is:

could you please think of any possible solution to avoid such a race condition and identify the email?

Answer 1

Why don't you use different e-mail accoouns for this (of course if you are not going to test the case when user try to login two times and mix codes/use proper codes from two messages e.g. on 2 devices)?

Answer 2

Some email providers let you use "+" on the email address, e. g. "[email protected]" that you can use to differentiate the different sources.

Is the information on the source of the email buried in the headers that you can hunt?

Can your devs embed a hidden element in the page you see immediately after the email is sent, then include either a similar hidden element in the email? Or in a header? Bonus points if they can do this only on your testing systems, or if you can change the URL to add a query string parameter to trigger adding the debug information?