In this recent post to his site Adam Wathan about writing your own custom test doubles (fakes) to help make your tests cleaner and improve their overall readability/maintainability.
Once in a while I run into a situation where trying to use a mocking library hurts the readability of my test. For example, say I’m building out a basic user registration flow where someone signs up and receives a welcome email. [...] To test that an account is created correctly, I can make a request to the endpoint and verify that the new account exists in a test database. [...] This covers creating the account itself, but what’s the best way to test the welcome email?
He goes through a few of the options that could be used to test this including using Mockery to replace the mailer class with a spy or actually sending emails. There's downfalls to both of these methods and he suggests using a custom "fake" where the mailer class is swapped out with an "in-memory" option with the same kind of interface. He does point out a few issues with this method, however, and offers a few tips to remember when using them.