[V3] File locking issue when writing to pact file with parallel tests in Jest

[mefellows]

Software versions

Please provide at least OS and version of pact-js

• OS: Mac OSX 10.15.7
• Consumer Pact library: 10.0.0-beta.29
• Provider Pact library: n/a
• Node Version: v12.18.0 (node) / 6.14.4 (npm)

Issue Checklist

Please confirm the following:

• I have upgraded to the latest
• I have the read the FAQs in the Readme
• I have triple checked, that there are no unhandled promises in my code
• I have set my log level to debug and attached a log file showing the complete request/response cycle
• For bonus points and virtual high fives, I have created a reproduceable git repository (see below) to illustrate the problem

Expected behaviour

Pact file is written correctly when tests are run in parallel.

Actual behaviour

• I have 6 tests and launch them in parallel by jest
• In 50% cases it false with error:
• (line and column numbers are different each launch)
• If I launch jest in one worker – no such an error. Looks like it is a kind of race condition.

Failure notice:

Failed to write pact to file - Failed to parse Pact JSON - EOF while parsing a string at line 386 column 20

The error seems to be this.pact.writePactFile(result.mockServer.id, this.opts.dir) // src/v3/pact.ts:208:23, and likely is a file locking issue.

Steps to reproduce

cd examples/v3/e2e
npm i --save-dev jest
cp test/consumer.spec.js test/consumer2.spec.js 
cp test/consumer.spec.js test/consumer3.spec.js 
cp test/consumer.spec.js test/consumer4.spec.js
jest test/*.spec.js

[TimothyJones]

In on mobile, but the documentation says somewhere that tests need to be run with —runInBand. We might need to surface that more clearly.

Of course, if we can fix it, that would be even better.

[mefellows]

Yes we do indeed! But that's only for the current package, the v3 package should be allowed to do this

[mefellows]

from mock_server.rs:

It seems the original author could foresee this issue :)

[TimothyJones]

I believe this issue will happen with any framework that parallelises tests- but Jest is the only one I am aware of.

I wanted to get jest-pact to detect whether the tests were running in parallel and warn, but I couldn’t figure out a way to determine it

[TimothyJones]

Oh, I didn’t see this was v3

[TimothyJones]

A coworker and I once chased a broken feature down to a function that said “todo: implement this method”. So I guess this is better ;)

[mefellows]

Ron, I can see you've been making some changes for this. I was also but haven't pushed. I'll leave the upstream lib changes for you, want me to push the updates to the JS side? FYI it was fairly easy to replicate by just duplicating more tests.

[uglyog]

Rust libs have been released

[TimothyJones]

@mefellows Do you know if this can be closed now?

[mefellows]

Yes, I believe it has been fixed - thanks and closing!