PubSub registry fails to start or race condition when testing? about phoenix_pubsub HOT 3 OPEN

I recently upgraded the pubsub dependency in my project following the documentation, but I am getting this error whenever I run the server:

an exception was raised:
** (ArgumentError) unknown registry: Demo.PubSub
(elixir 1.10.2) lib/registry.ex:1239: Registry.info!/1
(elixir 1.10.2) lib/registry.ex:920: Registry.register/3
(phoenix_pubsub 2.0.0) lib/phoenix/pubsub.ex:117: Phoenix.PubSub.subscribe/3
(phoenix 1.5.8) lib/phoenix/channel/server.ex:420: Phoenix.Channel.Server.init_join/3
(phoenix 1.5.8) lib/phoenix/channel/server.ex:378: Phoenix.Channel.Server.channel_join/4
(phoenix 1.5.8) lib/phoenix/channel/server.ex:298: Phoenix.Channel.Server.handle_info/2
(stdlib 3.7) gen_server.erl:637: :gen_server.try_dispatch/4
(stdlib 3.7) gen_server.erl:711: :gen_server.handle_msg/6

Here is my application.ex

def start(_type, _args) do
children = [
  {Phoenix.PubSub, name: Demo.PubSub},
  Demo.Repo,
  DemoWeb.Endpoint,
  {Demo.ExpireCodesJob, []},
  {Demo.DistributeCodesJob, []},
  {Oban, oban_config()},
  worker(PlugAttack.Storage.Ets, [Demo.PlugAttack.Storage, [clean_period: 60_000]])
]
    opts = [strategy: :one_for_one, name: Demo.Supervisor]
    Supervisor.start_link(children, opts)
end

It happens occasionally not all the time as other users reported.

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Hi there, I am facing similar issues, I had updated to version 2 and now I am confused, the code documentation establish this as a valid example - name as an atom {Phoenix.PubSub, name: :my_pubsub},
but the notes on the readme says {Phoenix.PubSub, name: MyApp.PubSub})

What's the correct one? my test suite is failing since multiple errors like ** (FunctionClauseError) no function clause matching in Phoenix.PubSub.broadcast/4 Any help is very appreciated :D

from phoenix_pubsub.

@sashaafm What does the test look like that is causing the issue? I know it's silly, but since you've confirmed pubsub is starting first in the supervision tree, is it possible there is a typo in the name MyAppServer.PubSub when you call broadcast? Also, if there is or isn't an alias present in that file, that's tripped me up in the past.
But yeah, likely the devil is in the details, and seeing the actual test implementation (or place where you call broadcast) might help.

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