Add style guide and code quality standards

[hasheddan]

What would you like to be added:

As the functionality and number of packages in krel continues to grow, we are starting to see divergence in how new features are implemented, tested, and maintained. We should add style guidelines and quality standards so that someone is completely new to the project can make contributions that are easily reviewed and integrated without degrading quality.

Why is this needed:

There are a few key areas that we have determined as important to maintain quality and consistency:

• Exposing the minimum required public API in packages (i.e. bias towards private fields in structs and interfaces)
• Follow pattern of "accepting interfaces, returning structs" (i.e Robustness principle)
• Avoid "testing through" (i.e. make your interfaces easily mockable)
• Generate mocks in a consistent manner (we use counterfeiter)
• Establish and measure a (potentially flexible) threshold for unit test coverage
• Establish what types of features require integration / e2e testing

This is not an all-inclusive list, but can serve as a good starting point for a document that we can continually iterate on.

/assign @hasheddan @saschagrunert

[justaugustus]

Thanks for opening this, Dan!
/priority important-soon
/milestone v1.21

[puerco]

+1 Thanks for pointing this out dan, I certainly would like to get some some of these well established (and understood!) to start implementing them. Sometimes I get lost and I feel waste too much time reinventing the wheel.

[saschagrunert]

@hasheddan when do we want to work on this issue? Seems not part of our roadmap planning but we may wire it into some side-effort.

[justaugustus]

Fun discussion w/ @wilsonehusin and some of the team on Twitter: https://twitter.com/stephenaugustus/status/1359354950019657730?s=20

Let's try and tackle this as a priority for v1.21.