I just spent half a day trying to figure out how to get around this:

(DBConnection.OwnershipError) cannot find ownership process for #PIDxxx

Most of the time was spent trying to find decent references. I didn’t find anything in the Ash docs itself, and the examples I did find made no mention of connection contention (in fact, the examples are very straightforward using ETS, so contention probably isn’t an issue…)

I’m thinking an edit to the Ash Testing topic would be nice…? Perhaps adding mention of how this can seemingly bite you out of nowhere (my simple app was fine, then “something happened,” it tipped over the edge I guess, and suddenly all my tests stopped working).

I’d be happy to do a PR. Haven’t done one before, imagine the docs in github somewhere…

All that said, before making said PR, wanted to double-check what I’ve learned, as this was new territory for me:

(DBConnection.OwnershipError) cannot find ownership process for pid … root cause

Ecto docs and a few posts quickly point toward shared connection contention, particularly when using async tests.

What confused me: Various posts / Ecto docs made it sound like turning off async: true would fix the issue. Not so that did nothing.

Other info led me to believe switching from a :manual to either :auto (nope) or :shared (doesn’t exist anymore) sandbox mode would help. (Neither did).

While both strategies are offered in the Ecto docs, neither did anything toward fixing the problem. ¯_(ツ)_/¯

Ecto docs are confusing

Just that. The Ecto.Adapters.SQL.Sandbox docs offer a few different strategies. The way I interpreted the docs, I should be adding this to my tests:

    setup do
      # Explicitly get a connection before each test
      :ok = Ecto.Adapters.SQL.Sandbox.checkout(WasteWalk.Repo)
      # Setting the shared mode must be done only after checkout
      Ecto.Adapters.SQL.Sandbox.mode(WasteWalk.Repo, {:shared, self()})
    end

That did fix the tests but left me with another problem. All kinds of Postgrex.Protocol (pid<0.404.0>) disconnected: ** (DBConnection.ConnectionError) cropping up (not just in my tests but a lot of framework tests). Made the situation worse.

What I settled on…

I ended up with just this in my tests:

    setup do
      :ok = Ecto.Adapters.SQL.Sandbox.checkout(WasteWalk.Repo)
    end

This is a new project – major upgrade from my last one (which used older Elixir, Phoenix, Ash). Didn’t have to worry about any of this “in the old days,” so… something new.

So far so good. Tests are working, nothing else has broken. I still don’t completely understand why it’s necessary (well, in theory, I suppose I do… more accurately, I don’t understand why turning on async:true didn’t solve the problem, nor why using a shared connection resulted in so much horrible fallout).

Anyhow, any further advice or explanation is welcome. Like I said, if there’s consensus this would be a good add for the docs I’ll do a PR. Hopefully with a better explanation than, “well, this fixed it, dunno why tho.”