Enable coverage reporting for emulator

[m-Peter]

Work towards onflow/developer-grants#132

Description

Allows developers to start the emulator with coverage reporting, which can be viewed in the browser, on this URL:

• http://localhost:8080/emulator/codeCoverage

The respective flag (--coverage-reporting) can be used like this:

flow emulator --storage-limit=false --coverage-reporting -v

It also adds an HTTP endpoint for flushing/resetting all the collected coverage report, on this URL:

• http://localhost:8080/emulator/codeCoverage/reset

This endpoint accepts only a PUT verb, at the moment. For example:

curl -XPUT 'http://localhost:8080/emulator/codeCoverage/reset'

Special thanks to @bluesign, for his great ideas 🙌
Special thanks to @turbolent, for his great reviews, which have unblocked this 💯

---

For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• Code follows the standards mentioned here
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[codecov-commenter]

Codecov Report

Merging #969 (451fec6) into master (3fc9e7e) will decrease coverage by 0.01%.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           master    #969      +/-   ##
=========================================
- Coverage    2.53%   2.52%   -0.01%     
=========================================
  Files           5       5              
  Lines         434     435       +1     
=========================================
  Hits           11      11              
- Misses        422     423       +1     
  Partials        1       1              

Flag	Coverage Δ
unittests	2.52% <0.00%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
internal/super/project.go	0.00% <0.00%> (ø)

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[devbugging]

@m-Peter should we merge?

[m-Peter]

@sideninja Yes, of course! We are just awaiting this to be included in a release, before publicly announcing the new features to the dev community 🙏

[devbugging]

@m-Peter could we add docs on this to the CLI, how you run it and maybe an example?

[m-Peter]

@sideninja I have created an entire repository with detailed usage of these new features: https://github.com/Build-Squad/flow-code-coverage/blob/385067c991608e7a37eba742bd857fab136ebeb0/README.md. I am just waiting for a new release of flow-cli to share it with the rest of the community. We can add afterwards more docs on every relevant repository. What is your opinion on this?

[devbugging]

@m-Peter sure that makes sense. The thing required tho is to document the flags as part of the CLI docs.

[m-Peter]

@sideninja Are you referring to this section? Because I don't see the test command there. I also found this document

[devbugging]

@m-Peter sorry for not making it clearer, what I meant was adding the docs for flags here https://github.com/onflow/flow-cli/blob/master/docs/run-tests.md
You can check other files in docs to see the format of documenting flags.

[m-Peter]

@sideninja Ah, thanks. I am already updating that document. I will ping you soon 🙏

[m-Peter]

@sideninja I have added two more commits regarding documentation:

• 451fec6
• a396b2c

I will also open a PR on the flow-emulator repository, to address the new --coverage-reporting flag that was recently added.

[devbugging]

@m-Peter looks good. Let me merge and I can make a release EOT.

[m-Peter]

@sideninja That would be great 💯
Here's the companion documentation PR, for flow-emulator onflow/flow-emulator#354