jest: open handle detected

Hi all, I would like to report a strange behaviour that started to happen after upgrading to the latest release. When running our test suite, I noticed a warning message after completion saying:

Ran all test suites matching /src/i.

Jest has detected the following 1 open handle potentially keeping Jest from exiting:

  ●  MESSAGEPORT

      at Object.<anonymous> (../../node_modules/node-domexception/index.js:6:12)
          at async Promise.all (index 16)
          at async Promise.all (index 3)
          at async Promise.all (index 1)
      at TestScheduler.scheduleTests (../../node_modules/@jest/core/build/TestScheduler.js:333:13)
      at runJest (../../node_modules/@jest/core/build/runJest.js:404:19)
      at _run10000 (../../node_modules/@jest/core/build/cli/index.js:320:7)
      at runCLI (../../node_modules/@jest/core/build/cli/index.js:173:3)

Doing a rollback to node-fetch@3.1.1 makes the warning disappear. I would assume that something has changed in the latest release that is causing this issue.

Reproduction

Steps to reproduce the behaviour:

1. Create a test file that uses node-fetch
2. Run the test with jest

Expected behaviour

I would expect to not have any warning/error in the jest output

Screenshots

Your Environment

software	version
node-fetch	v3.2.0
node	v16.13.0
npm	8.1.0
Operating System	macOs Monterey 12.1

[apoco]

For what it’s worth I’m also experiencing this with node-fetch@2.6.7 and node@16.13.0.

Jest has detected the following 5 open handles potentially keeping Jest from exiting:

  ●  TLSWRAP

      187 |
      188 |     it("my test", async () => {
    > 189 |       const res = await fetch(url, {
          |                              ^
      190 |         agent,
      191 |         method: "PATCH",
      192 |         headers: {

      at node_modules/node-fetch/lib/index.js:1468:15
      at fetch (node_modules/node-fetch/lib/index.js:1437:9)
      ...

…and I just now realized that in all cases they’re tests where I have a request body and the server responds with an error. It appears that the request stream is not aborted after the server responds.

[salemhilal]

I had the same problem as above (the MESSAGEPORT one) with essentially the same stack trace. I thought it must have something to do with the node-domexception polyfill that node-fetch uses. The open handle error points to the line where the new MessageChannel is created in the polyfill, but patching the polyfill to explicitly close its ports (i.e. port.close()) didn’t fix the problem.

It turns out I was starting the web server I was about to test more than once, inadvertently. I wasn’t closing the extra instance, which caused my tests to hang. Something about Jest’s open handle detection doesn’t like that MessageChannel hack, but it seems like Jest’s detection is also a bit of a red herring. Fixing the server problem caused my tests to pass without any open handler warnings, no changes to node-fetch necessary.

I’m leaving this message as a bit of a warning to other people; if you think it’s node-fetch, pick through your code again and see if you’re not inadvertently missing something.