Test setup improvement and more tests

This module has very little tests or no tests at all for some scenarios. There is need for movement from "production tested" to improved test system.
I think that this module needs following tests

Module promises:
- Module promises reconnection and Error handling. **no tests**
- Tests for continuous health checks. **no tests**
- Proper error handling **very little tests**

Other tests could be:
- "Stress testing". Trigger hundreds or thousands events in Postgres db and handle events
- Test for module imports (commonjs, es6 import)
- listen many channels with single subscriber