Add pipeline Kernel tests

Just want to see if this will get tested.

Add a fix for the config schema

Added those tests from core that should generally make sure that we've not broken core functionality.

Need to add our tests.

Here's an overridden core simpletest to see if this sort of thing will work.

Copy over all of the tests.

Now that we have the core tests, we should actually write some tests that use pipelines too.

I think I'll need this to be a Kernel test.

Rough plan of what could be tested;

• Have a test image processor plugin that strips metadata or just truncates the file to zero bytes or somesuch
• Spin up an image pipeline and add no processors to it
• Spin up an image pipeline and add an instance of the test image processor
• Apply both of the above pipelines to an image file in a virtual filesystem, asserting that the first does nothing, and the second does what its supposed to do.
• unit test each of the image processors to assert that the correct command is called given all the options etc.

Here's a very initial unit test just for a single invocation of advpng, just to make sure I'm writing them in the correct way for d.o to run them.

Hmm...fairly certain that drupal.org didn't actually find the test added in that patch.

Try putting the test file in the correct location.

That's better, now need to make the test actually do something.

Adding a base class for the tests, and tests for AdvDef and AdvPng

Fixup those tests, hopefully.