perf(mocha): run tests in parallel

[curbengh]

What does it do?

A new feature of mocha@8. Consistently 3s faster in my single-core VM.
nyc (for now, v15.1.0) doesn't support mocha's parallel mode yet, so parallel mode is disabled in test coverage job.

How to test

git clone -b parallel-mocha https://github.com/hexojs/hexo.git
cd hexo
npm install
npm test

Screenshots

Pull request tasks

• Add test cases for the changes.
• Passed the CI test.

[curbengh]

it's not reliable yet, unit test sometimes fail with:

  1) Hexo
       Console
         generate
           update theme source files:

      AssertionError: expected 'b' to deeply equal 'bb'
      + expected - actual

      -b
      +bb
      
      at Context.<anonymous> (hexo/test/scripts/console/generate.js:207:22)

[SukkaW]

it's not reliable yet, unit test sometimes fail with:

Appears that failed tests are related with fs operation.

[curbengh]

nyc is currently incompatible with mocha parallel mode, can confirm in my machine.

[SukkaW]

@curbengh We can run coverage only once, while the other tests can be still run in parallel.

[curbengh]

We can run coverage only once, while the other tests can be still run in parallel.

Mocha supports environment variable MOCHA_PARALLEL=0. It should be possible to disable it in coverall job.

---

Edit: Apparently not...

[curbengh]

Currently, coverall is executed in every job. Perhaps can migrate to a dedicated job?

[SukkaW]

Perhaps can migrate to a dedicated job?

+1

[coveralls]

Coverage decreased (-0.03%) to 98.238% when pulling 110cdc6 on curbengh:parallel-mocha into 5b2808c on hexojs:master.

[curbengh]

in previous draft, this job is integrated into tester job with if: ${{ matrix.os == 'ubuntu-latest' && matrix.node-version == '12.x' }}, but then tester would have one extra mocha execution which defeats the purpose.

[SukkaW]

LGTM!