Write proper unit tests

[troccoli]

Some of the unit tests are really integration tests as they rely on data to be created.

For example, Tests\Unit\Models\TeamTest::testItGetsTheFixtures relies on clubs and fixtures to be created. I understand this being a unit test for a model and this particular test actually testing the relationship between the Team and the Fixture models, it will be difficult to refactor. However we should have a look at all unit tests and write them as such. If it not possible, as it seems it is the case for Tests\Unit\Models\TeamTest::testItGetsTheFixtures, then the test should be moved in the Integration folder (or Feature folder, depending on #110).

We should also make sure we use Events::fake() in many of those tests so that when a model is created we don't fire the event (which we listen to to create roles and permissions).