Add ability to turn on test mode dynamically (for testing).

[r-kujawa]

Describe the solution you'd like. ✈️

Just like other laravel services, you should be able to call a fake() method on the service to start mocking behaviour.

What problem will this solve? 🔥

Simplifies testing.

Additional context 💬

A good example of this is the Queue facade, you may call Queue::fake() and it will start mocking the queue's asyncronous behaviour.

Which version(s) should this be pointed at?

1.x