Write tests for all submodules

Let's do this later. Definitely useful, but for example we'll have to mock the SDK.

@grevil: As long as you're "in" the module, could you write a short list, which tests might make sense here and how?

I think we'd need to mock the SDK, that should make it easy to track most of the functionality. I think this would be a great learning for us. Still minor.

Sure!

We need:
Kernel Tests for the PHP SDK
Simple javascript test, that the posthog js is loaded
Tests for the alter hook (if possible)

I think the other submodules are not easily testable, Maybe we could somehow "snatch" the event parameters send to posthog, but I am unsure, whether this is easily done.