[Laravel 6] Add support for Laravel Dusk tests

[bennothommo]

Forms part of work done in #4893. Replaces #3051.

This implements support for Laravel Dusk, a more friendly way for doing comprehensive browser-based testing.

This PR significantly refactors the testing base to allow these tests to be included for both core, as well as a part of plugins.

[LukeTowers]

LGTM! Still need a PR to the docs documenting all this stuff now and an update the L6 upgrade guide

[LukeTowers]

@bennothommo

If you are manually registering Dusk's service provider, you should never register it in your production environment, as doing so could lead to arbitrary users being able to authenticate with your application.

How can we protect users from this?

[bennothommo]

@LukeTowers There's a couple of things in play already to prevent this from happening:

• We're using automatic registration of the service provider, via using autoload-dev in composer.json.
• The tests run in a different environment to the live site by replacing .env with .env.dusk on the fly, as well as the configuration in config/dusk/. The database runs in SQLite for the tests by default, and requires manual intervention in order to use any other database.

It could be possible that with that message, they're referring to the Dusk routes they provide in their service provider, which can basically let you log in as any user. They don't actually work with October, so we could potentially extend the Service Provider and just remove those routes.

[LukeTowers]

@bennothommo I would feel most comfortable if we removed those routes entirely.

[bennothommo]

@LukeTowers instead of extending the service provider, I've just disabled auto-discovery for Laravel Dusk, and am using the system module's service provider to load the console commands as necessary. Those routes should no longer be loaded.

[bennothommo]

This is ready to review and merge into the main L6 branch. I'll add the tests/README.md changes to the October docs once reviewed.

[LukeTowers]

LGTM!

[LukeTowers]

@bennothommo actually have we dealt with re: unit tests related to rainlab/translate-plugin#509 & rainlab/translate-plugin#546
DatabaseServiceProvider does the following when registering:

Model::clearBootedModels();
Model::clearExtendedClasses();
Model::flushDuplicateCache();

Should we also add Model::flushEventListeners(); (used in https://github.com/octobercms/october/blob/master/tests/unit/cms/classes/CmsCompoundObjectTest.php for Halcyon, but also applicable to Eloquent) and then also implement a Model::flushDuplicateCache() in Halcyon models and add those four lines to HalcyonServiceProvider?