failed to start child: Mneme.watch.TestRunner

[tcoopman]

I'm a bit bumped. I was running mneme.watch just fine, and suddenly I get this all the time:

mix mneme.watch
** (EXIT from #PID<0.95.0>) shutdown: failed to start child: Mneme.Watch.TestRunner
    ** (EXIT) an exception was raised:
        ** (ArgumentError) could not fetch application environment :after_suite for application :ex_unit because the application was not loaded nor configured
            (elixir 1.17.2) lib/application.ex:778: Application.fetch_env!/2
            lib/ex_unit.ex:460: ExUnit.after_suite/1
            (mneme 0.9.2) lib/mneme/watch/test_runner.ex:40: Mneme.Watch.TestRunner.init/1
            (stdlib 6.0) gen_server.erl:2057: :gen_server.init_it/2
            (stdlib 6.0) gen_server.erl:2012: :gen_server.init_it/6
            (stdlib 6.0) proc_lib.erl:329: :proc_lib.init_p_do_apply/3

running mix test works fine

This is on mneme 0.9.2

[zachallaun]

Hmm... There are some scenarios in which mneme.watch has to run System.restart(), which unloads applications. I have an idea for a fix. A couple questions:

1. It happens consistently now, every time you run mix mneme.watch, even from scratch? Or does it run the first one fine, and then fail on reload?
2. Try deleting _build/test; does it still fail?

[tcoopman]

1. it was on every run consistently
2. deleting _build/test fixes it again

[zachallaun]

Okay, thanks! Knowing that deleting _build/test fixes it may help me reproduce the issue.

[tcoopman]

it reproduces for me quite easily.

I run mix mneme.watch --stale then kill it with ctrl+c and then the next time it crashes.

I'll see if it happens on other params to mneme.watch as well

[zachallaun]

I'm not able to reproduce it yet, even using --stale. Since you can reproduce, could you please try:

1. Get mneme.watch into the bad state, such that running mix mneme.watch --stale immediately crashes with the :ex_unit config error
2. Instead of deleting all of _build/test, delete only _build/test/lib/YOUR_APP/.mix/mneme.watch.restart
3. Run mix mneme.watch --stale and check whether the crash persists

[zachallaun]

@tcoopman Actually, I think the fix might be simpler than I thought. Could you please try this branch and let me know if the problem persists?

{:mneme, github: "zachallaun/mneme", ref: "za-issue-95", only: :test}

[tcoopman]

@zachallaun thanks, that seems to fix it, will keep running that for now.

Regarding your previous suggestion:

1. It's the same on mix mneme.watch as well
2. I don't have _build/test/lib/YOUR_APP/.mix/mneme.watch.restart, only these:

├── cached_dot_formatter
├── compile.app_cache
├── compile.elixir
├── compile.elixir_scm
├── compile.lock
└── compile.protocols

[zachallaun]

Glad that fixes it!

I'll publish a release for this and #96 momentarily.

[zachallaun]

Will publish v0.9.3 once CI completes on main.