Guide for developers: how to test KIC

[mflendrich]

Is there an existing issue for this?

• I have searched the existing issues

Problem Statement

Broken out of #4099

As a developer I would like to know what level/method of testing (unit, integration, e2e) is appropriate for the behavior change/functionality I'm implementing.

It is tempting to write an integration/e2e test where a unit/env test would suffice (and be faster, easier to comprehend and maintain).

Proposed Solution

• Provide definitions of existing testing levels (unit, envtest, integration, e2e) and their characteristics/performance
• Idea (@czeslavo):Provide a flowchart / decision tree to help decide on the testing level

Additional information

For the flowchart, example by @randmonkey:

Does it need Kong gateway?
Yes -> integration test
No -> unit test

Acceptance Criteria

• Developer documentation defines all existing testing levels
• Developer documentation helps make a decision about the testing method most suitable to fix the problem

[pmalek]

Some info about testing has been put into https://github.com/Kong/kubernetes-ingress-controller/blob/5d8abcae128ce355afb74d261baba5672a4e40c0/TESTING.md

[rainest]

For whatever reason merging the linked PR did not close this issue despite Github saying it would. Closing manually.