[WIP] Integration testing

Created the basics to run the tests and implemented the delayed_jobs tests. The ways testing works is you schedule jobs, you ask the adapter to run the jobs and them make assertions. My first try was to start an actual adapter worker process but it's gets complicated and it will increase greatly the runtime.
This is still WIP and I'll add more adapters as I find time and solutions to run the jobs (delayed_jobs is easier as it supports this built-in .. the `work_off`).