Create `How to create a unit test and implements with github action` documents

[kim201212]

Checklist

• [ ] New Feature for the SVC/Plugin
• [ ] New Feature for CI/CD
• [ ] Enhancement on Vatz

• [x] Others(etc. e.g, documentation,...)

Please describe, what it's about or related Problem with

A clear description of what feature need to be developed or enhanced in Vatz

=> We haven't decided how to do the unit test.

Describe the output that you are expecting for above

A clear and concise description of what you expect to happen.

=> If possible, make unit test possible on vatz-plugin.

Describe alternatives you've considered

A clear and concise description of any alternative solutions or features you've considered.

=> Document what code makes it possible.

Additional context

Add any other context or screenshots about the feature request here.

[xellos00]

@kim201212 There are two requirements for this issue prior to create the documents on gitbook. Please, ping me if you need further discussion for following items.

1. Develop sample unit test for each module's function in interface

   which registered issue

   • 85

Ex) HealthCheck module

2. Create a CI/CD to do unit-test through github action when PR has requested.

   Unit Test must passed when PR request or before release.
   I didn't ask this previously, because when you finish first item, I will ask this item as well after.

I think it is good to start with #85 and #120 on Sprint 9 if you don't mind.