Add generator command tests.

[tsommie]

Thanks to everyone maintaining this package, I wonder why Tailor is yet to add repositories to Laravel. After years of using this package, I decided to contribute to it but first I needed a safety net to make sure I don't break anything.

This PR includes tests for the generator command classes only.
This PR does not include tests for the eloquent repository class.

Few suggestions:

• The Laravel community is changing and considering how opinionated this package is, it has become a little unintuitive to use. Considering the introduction of Inertia.Js and Livewire it is safe to say that the nake:entity command is not very flexible.
• Different branches should be created to support different versions of Laravel and not have every release support all versions of Laravel since version 5.
• Committing the composer.lock file is not neccessary.