Allow Traits to define modules for install during tests

Is there an example test that needs that could be converted.

This might be better defined as a feature request.

Let’s see what committers think!

I'm not sure about this one. Drupal is really special in how we futz with the autoloader to make test traits autoloadable (and in fact all the tests). This is not normal behaviour.

The issue summary needs to be updated with a concrete use case of why this is or might be a good idea. Atm the issue summary is just about why you can't do it not why to do it.

I updated the Issue summary with some more detail.

Sorry to be late to the conversation, but should traits declare dependencies? I always thought of traits as helper functions or common stuff. But if I have multiple tests that need specific setup then I make a test base file.