The beginnings of a useful testing framework

[jamiebrynes7]

Description

This PR condenses some of the patterns we've used in testing into a MockWorld class which helps you write integration tests in a fluent and easy to understand way. The goal of this was to make it very easy to spin up the full stack with a mock connection and tick through frames. This is visible in the API which looks something like:

MockWorld.Create(new MockWorld.Options())
	.Step(world => /* first frame */)
	.Step(world => /* second frame */)
	...

The MockWorld classes has a minimal feature set, and can be extended in the future:

• Handling the creation and management of the world & player loop.
• Create and link GameObjects (with a given component), a future extension could be adding a <T1, T2> & <T1, T2, T3> version.
• Passing arbitrary context through 'frames' simply by returning an object in the lambda. This context will be passed through any number of frames until it is replaced:

   MockWorld.Create(new MockWorld.Options())
   	.Step(world => 10)
   	.Step((world, number) => /* do something with number */)
   	.Step(world => /* do something without number */)
   	.Step((world, number) => { /* do something with number */ return "foo"; })
   	.Step((world, str) => /* do something with string */);

This is all wrapped up in the MockBase abstract class which test fixtures can inherit from. This has a simple SetUp and TearDown where the World is created and then disposed so each test can have a fresh world to start with.

I've ported the existing tests in the Test Project to this new paradigm, there are tests in Core that would benefit from this API but we may want to move around the location of the Mock* objects in order to use them there.

Commits are ordered!

Tests

Old tests ported & still passing.

Documentation

• Changelog

[zeroZshadow]

Its a little unclear why this test works the way it does. Can we somehow make it clearer that this works because the BasicEntity does not contain the component that the monobehaviour here has a reader for?.

[jamiebrynes7]

I'd rather not change the tests themselves in this PR

[zeroZshadow]

LGTM, dont forget the changelog

[paulbalaji]

Love it

[jessicafalk]

I really like it :D