Plugin-registerable self tests

[grittyfrog]

plugin-self-test.webm

(apologies for the terrible framerate)

The goal of this change is to let plugins register their own self-tests.

We do this through the ISelfTestRegistry interface. For a plugin it would look like this:

[PluginService]
public ISelfTestRegistry SelfTestRegistry

// Somewhere that gets called by your plugin
SelfTestRegistry.RegisterTestSteps([
  new MySelfTestStep(),
  new MyOtherSelfTestStep()
])

Where MySelfTest and MyOtherSelfTest are instances of the existing ISelfTestStep interface.

The biggest changes are to SelfTestWindow and the introduction of SelfTestWithResults. I wanted to make sure test state wasn't lost when changing the dropdown state and I was finding it a bit annoying to work with the Dictionary now that we can't just rely on the index of the item.

To fix this I moved all the "test run" state into SelfTestWithResults, most of the changes to SelfTestWindow are derived from that, other then the addition of the combo box.

The documentation for this service is a bit sparse, but I wanted to put it up for review first before I invest a bunch of time making nice documentation.

I'm keen to hear if we think this is useful or if any changes are needed.

[goaaats]

There's a new warning in the window class, looks good though otherwise.
Echoing Hasel's concern from Discord, what happens when a plugin unloads while its tests are selected? Ideally you wouldn't copy the tests into the window class, you are not allowed to keep references to objects that belong to the plugin around, but I'll leave it up to you :)

[grittyfrog]

I'll address the feedback tomorrow, thanks for taking a look! 🙂

[grittyfrog]

Updated the PR in response to all the feedback:

• When a plugin is unloaded the SelfTestWithResults class now disposes of the ISelfTestStep reference, this should prevent any errant plugin derived class references from sticking around
• When a plugin is unloaded the self test group is now marked as "Unloaded" in the window. We show an icon and unload all the tests, but it remains selected and available in the dropdown
• When a plugin is reloaded the self-tests will automatically repopulate
• Added docstrings to everything and an example to ISelfTestRegistry (since stylecop complained)

There was also a ton of stylecop errors in the previous PR which I have fixed. Please let me know if there's any other issues with this change 🙂

[goaaats]

Thanks, looks great!