Where do I put configuration files for testing? Hopefully, this will be a simple question.

I am writing a kernel test for a class, called FooConfig, that reads from a configuration file. For the purpose of facilitating this test, I need a configuration YAML file that exists purely for testing.

So the question is: is it best practice for this configuration file to live under config/install, or should it exist within the /tests directory?
One way is to create a small testing module that contains specific config you need for a test, then have the test use it as a dependency. In my case, I put that module itself under the tests directory and marked it as hidden in its info file.

Although a drawback would be keeping these config files up to date when the system changes - but failing tests should point you in that direction too.

For Kernel tests be sure to call and install the test modules config.