Unit testing concurrent software - what do you do?

Question

As software gets more and more concurrent, how do you handle testing the core behaviour of the type with your unit tests (not the parallel behaviour, just the core

Answer 1

Unit tests really should not test concurrency/asynchronous behaviour, you should use mocks there and verify that the mocks receive the expected input.

For integration tests I just explicitly call the background task, then check the expectations after that.

In Cucumber it looks like this:

When I press "Register"
And the email sending script is run
Then I should have an email