Hello everybody!

I’ve discovered property-testing with stream_data a few months ago. Since then, I’ve successfully re-written the tests of a library, and I’m willing to use property-testing everywhere I can.

I’ve tried to property-test a Phoenix context boundary, but I’m facing performance issues:

defmodule Kakte.AccountsTest
  use Kakte.DataCase

  alias Kakte.Accounts
  alias Kakte.Repo

  [...]

  property "list_users/0 returns all users" do
    # user_attrs/0 is a generator for valid user attributes.
    check all attrs_list <- uniq_list_of(user_attrs(), length: 5) do
      Repo.transaction(fn ->
        users =
          Enum.map(attrs_list, fn attrs ->
            {:ok, user} = Accounts.register(attrs)
            user
          end)

        users_list = Accounts.list_users()

        assert length(users) == 5
        Enum.each(users, fn user -> assert user in users_list end)

        Repo.rollback(:done)
      end)
    end
  end

  [...]
end

Running this test takes more than 2.5 seconds on my machine. I know a property-test is expected to be longer to execute due to higher number of tests, but 2.5 seconds for one test is way too long IMO. I’ve tried to replace the test body by assert true and it runs quick, so I presume this is due to many repo transactions, but maybe I am misleading.

I have basically three questions:

1. Is it a good idea to use property-testing everywhere?
2. Do you property-test your Phoenix applications?
3. How can I manage to speed up this test?

For information, the context source is here on GitHub.