Add tests

[agis]

• [x] e2e/worker: passing but flakey suite (requeues)
• [x] e2e/worker: passing suite
• [x] e2e/worker: failing suite
• [x] providing a specific file
• [x] providing a different spec folder
• [x] job scheduling + file splitting
• [x] non-example error (e.g. syntax error)
• [x] concurrent workers (can we do this transparently for all test cases?)
• [x] reporter
• [ ] worker liveness
• [ ] CLI generic flags (worker, build, redis)
• [ ] custom .rspec file in project root (not important)
• [x] find a way to silence stdout of workers