"Cannot set property 'err' of undefined" error occurs in place of other errors during automatic test-reruns on file save.

Current behavior:

When running tests locally through cypress open, and when interrupting tests by saving files (forcing a re-run), any failures occurred during the run can trigger this message:

The following error originated from your application code, not from Cypress.

  > Cannot set property 'err' of undefined

When Cypress detects uncaught errors originating from your application it will automatically fail the current test.

This behavior is configurable, and you can choose to turn this off by listening to the uncaught:exception event. Learn more

The error is not really originating from the application; it’s occurring within hookFailed at https://github.com/cypress-io/cypress/blob/4cfcae28f097e013ffe7dc7419905eccf1022709/packages/driver/src/cypress/runner.js#L526. Both getTest() and getTestFromHookOrFindTest(hook) end up returning undefined.

I’ve seen this on two very different projects.

• At work, which is a custom server + Webpack setup, webpack/React, running on MacOS.
• At home, on a personal project running Next.js, running on Windows (Powershell). This project is linked below.

Desired behavior:

The test fails with the normal readable stack trace.

Test code to reproduce

This is easily reproducible on this project (created a branch with a failing spec): https://github.com/primitiveconcept/ludumdare46/tree/cypress/err-of-undefined/client

• Run npm run cy:dev for server + Cypress
• Run the filesystem.spec.ts spec
• Save the filesystem.spec.ts while the test is running. Reproduces around 25% of the time, may require a few tries.

If needed, I can try to come up with a minimal reproduction, but this isn’t a very complex project. The server isn’t required for the tests.

Versions

Cypress versions: Can reproduce on 4.9.0. Cannot reproduce on 4.5.0. Other versions are unstable for various reasons on the example project. At work, this started occurring on 4.6.0. OS: MacOS + Windows Browser: Chrome + Electron

[crfrolik]

The bug is annoying, but I’m more concerned that the error message is lying to us, implying that the error came from our code when it really came from cypress. Should there be another issue to address that?

[kuceb]

I’m working on this. We might have already fixed as part of https://github.com/cypress-io/cypress/pull/8113 (unfortunately didn’t make it into last release), and I’m working on getting a reproducible test case to verify