docs: add testing framework document

[nghuyenthevinh2000]

Summary of changes

Closes: #69

I add this pr so that we can comment directly to where changes are needed

cc: @ZaradarBH @inon-man @fragwuerdig @edk208

Report of required housekeeping

• Github issue OR spec proposal link
• Wrote tests
• Updated API documentation (client/lcd/swagger-ui/swagger.yaml)
• Added a relevant changelog entry: clog add [section] [stanza] [message]

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(FOR ADMIN) Before merging

• Added appropriate labels to PR
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)
• Confirm added tests are consistent with the intended behavior of changes
• Ensure all tests pass

[inon-man]

This is great. We have to learn from mistake. If we had time, measures should be taken, and prevent similar problems from recurring.

[nghuyenthevinh2000]

let's get this rolling