Running async tests with Hound?

I’m using Hound with ChromeDriver and I’ve read that it is possible to run async tests (e.g. multiple browsers executing the test cases in parallel). However, I can’t find any examples/tutorials how to do this.

There’s a question on StackOverflow that was kind of a starting point, but I was still getting DBConnection.OwnershipError exceptions or other timeout errors. Then I saw this answer in the forum saying that Wallaby/Hound support async tests through a plug found in Ecto.

Could someone provide a short example how to get this working? Thanks a lot in advance!

Elixir 1.4 / Phoenix 1.3rc

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Documented here:


@josevalim Thanks for the quick response, that was very helpful! I’m surprised Hound’s README doesn’t have a link to it. However, I’m still struggling to get this to work the way I think it should be.

I’ve got two tests, and when ran individually, they take ~15 seconds each (or ~30 seconds with mix test --only integration). After I added async: true I can see two Chrome browsers starting off, but strangely the total time with the async options and changes is still ~30 seconds, same as before, which seems wrong.

How could this be, is there something I’m missing? I followed the guide in the link carefully, and only made 1 change in the setup of my IntegrationCase file, due to an error:

defmodule MyApp.Web.IntegrationCase do
  use ExUnit.CaseTemplate

  using do
    quote do
      use Hound.Helpers
      import MyApp.Web.Router.Helpers
      import MyApp.Web.IntegrationCase

      @endpoint MyApp.Web.Endpoint


  setup do
    :ok = Ecto.Adapters.SQL.Sandbox.checkout(MyApp.Repo)
    metadata = Phoenix.Ecto.SQL.Sandbox.metadata_for(MyApp.Repo, self())
    Hound.start_session(metadata: metadata)
    # Added :ok since `start_session/2` returns a string.
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Tests in the same module do not run concurrently. Only tests in separate modules/files. I.e. the granularity of concurrency is per module and not per test. That’s because tests in the same module/file are usually exercising the same area of the codebase and would not benefit of concurrency.

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I see — to clarify, the tests are indeed split in two separate files, and each file has its own module, e.g.:

defmodule LoginTest do
  use MyApp.Web.IntegrationCase, async: true
  # ...

However, they do exercise the same main web application, just doing different things (one tests logging in, the other tests creating data). Would that mean that I cannot run them concurrently?

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Hi @svilen,

Wondering if you were able to get Hound to work with an async test suite using ChromeDriver? I’ve struggled for days trying to get this to work before punting and running everything synchronously and was reminded about it this morning: Async Hound tests failing sporadically with ChromeDriver


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@tme_317 No, sorry, I had to put this aside and leave them running sequentially.

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I recently used Hound as part of a GenStage pipeline (and spawned about 15 of this particular stage to run concurrently) and this is the code that worked well for me. I think you could create a GenServer and do the same (spawn a process for each test so they are fully isolated).

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