Adding more unittests

[antonykamp]

Describe the improvement you'd like It would be great to use more unittests. At the moment, we use the blitzjs default tests only. Additional tests testing

• mailer
• mutations
• queues
• the entire process XD

would help the project 🙃

Additional context Blitzjs uses @testing-library/react with jest. This is certainly worth a look 😅