[Bug]: Code execution does not break in debugging tool when watch mode is set

[cdoublev]

Version

29.6.1

Steps to reproduce

1. Clone my repo at https://github.com/cdoublev/jest-issue
2. node --inspect-brk=0.0.0.0:9222 ./node_modules/.bin/jest --watchAll (npm test)
3. Open chrome://inspect/ in Chrome
4. Click inspect in the target list

Expected behavior

I expect the code to break at the debugger line in ./add.js.

Actual behavior

The code did not break.

Additional context

I run the above steps in a virtual machine. I connect to the VM from my terminal with a SSH tunnel localhost:9222 -> 0.0.0.0:9222.

I have not checked if the problem occurs without the SSH tunnel because I am using a virtual machine so I do not have to install NodeJS on my machine's OS.

But I guess this problem is specific to this context, and is related to this change in version 29.6.0:

[jest-core] Always use workers in watch mode to avoid crashes (#14059)

Indeed, the code breaks when removing --watchAll from the command line arguments.

Environment

System:
  OS: Linux 6.1 Debian GNU/Linux 12 (bookworm) 12 (bookworm)
  CPU: (1) x64 Intel(R) Core(TM) i7-3612QM CPU @ 2.10GHz
Binaries:
  Node: 20.3.0 - /usr/bin/node
  npm: 9.6.7 - /usr/bin/npm
npmPackages:
  jest: ^29.6.1 => 29.6.1

[mrazauskas]

Seems like you are right about #14059. After it landed workers are used always instead of sometimes in watched mode. This means that your reproduction now fails always, but before it was failing sometimes. If I didn’t miss something. Might be that all worked as expected with --runInBand flag, but you are not mentioning it. (EDIT: Nope, see #6683)

All examples in debugging documentation use the --runInBand flag. The CRA example additionally sets --watchAll=false.

The configuration examples in vscode-jest repo also set --runInBand and --watchAll=false.

All this makes me think that it can be that the watch mode is not designed to work with debugger. For some reason. Can’t proof that.

@benjaminjkraft Could you take a look? I can’t recall if we did talk about respecting --runInBand in the watch mode? Does that make sense? (Sorry about the noise, I forgot about #14085.)

[cdoublev]

So the watch mode and debugging tools only worked together if --runInBand is set or if only one available core is detected? Curious to know why. There is nothing in the current version (v29.5.0) of the documentation about this.

The VM I am running Jest in has only one core (Virtual Box's default) therefore it always worked.

edit: there is a note explaining why --runInBand is somewhat mandatory for debugging, and #14085 seems to address my issue, therefore I am closing it.

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