How to configure for mocha parallel ?

[Shelvak]

Hi there, I'm trying to setup my env with parallel testing (because all my tests take about 4 minutes) and I was able to improve the time to 40seconds with last mocha version, but I can't get solidity-coverage run in parallel.

What I'm using:

• Hardhat: 2.6.0
• Mocha: 9.1.1
• solidity-coverage: 0.7.16

Commands:
Parallel: npx mocha
Sequential: npx hardhat test (or npx hardhat coverage to get the coverage)

My .mocharc.json:

{
  "parallel":   true,
  "jobs":       4,
  "slow":       "1500", // 1.5s
  "full-trace": true,
  "bail":       false,
  "inspect":    true,
  "timeout":    20000,
  "exit":       true,
  "require":    ["hardhat/register", "solidity-coverage"] // tried with `solidity-coverage/api` and others but nothing happened
}

Already tried with mocha: option in the .solcover.js but it runs sequentially with npx hardhat coverage.

Mocha requiring hardhat/register starts X processes and then run everything:

It's more a question than an issue but it would be awesome if we can get coverage working with mocha parallel =)

Cheers.

[cgewecke]

Hi @Shelvak. There's isn't any built-in support for parallelism via mocha. There are recipes for parallelizing jobs in CI here:

• SetProtocol
• Synthetix

(These suites are huge - in the 30-40 min range without parallelization)

The technique used there is:

• partitioning the test suites into several groups by name
• spinning up a process for each group and running the coverage task
• aggregating the coverage.json files produced for each job using a tool called istanbul-combine-updated in a final step

[cgewecke]

Another note - it's possible to configure the istanbul coverage report folder name in the .solcover.js options. This could be useful for a cli solution that's aggregating reports at the end.

[Shelvak]

Awesome cgewecke, thank you so much for the quick response. I think that I could hook the coverage part in each setup fork and try the merge report after everything. If I succeed I'll post here how I did it=)

[cgewecke]

Ok great!

[Shelvak]

Just in case anyone arrives here looking for "the answer". I solved this with docker (because parallel hardhat network fails most of the time):

• Create the project docker image
• Mount a "shared" coverage directory
• Run tests inside multiple dockers and copy the report with a custom name in shared directory
• Combine reports within the shared dir with istanbul-combine

Run parallel test inside docker:
https://gist.github.com/Shelvak/d0c753ea373d8a6f88a30a98e503d63b

I'm 100% sure that the scripts can be improved but it's working =P

Cheers

[cgewecke]

Closing in favor of #691