You can't test code that calls exit()
PHP's exit construct stops the process before your assertions can run. Mantle Testkit's terminate_request() preserves the same terminal behavior while turning the response into something your tests can inspect.
writing
Notes from the build log
Long-form notes on WordPress at scale, PHP tooling, and the unglamorous work of keeping large publishing systems boring.
Lockdown WP Admin
An older plugin of mine on .org.