$ vendor/bin/phpunit contentbank/tests/contentbank_test.php --filter test_is_context_allowed --process-isolation

Moodle 4.2beta (Build: 20230414)

Php: 8.0.28, mysqli: 8.0.32, OS: Linux 5.4.0-146-generic x86_64

PHPUnit 9.5.27 by Sebastian Bergmann and contributors.

Serialization of 'Closure' is not allowed

The test case never completes, because PHPUnit crashes during the run

It's related to a "feature" (bug?) within PHPUnit that is described at https://github.com/sebastianbergmann/phpunit/issues/2739 - caused by the following:

1. Test using a @dataProvider;
2. @dataProvider returns a closure/callable;
3. Running with --process-isolation

Grepping the codebase, it seems we hit this only in contentbank tests (I didn't find any other cases that would trigger it)