Cannot find mock/stub in process #PID<0.512.0> using Req

I have a simple GenServer making an HTTP request

defmodule GamePlay do
  use GenServer

  alias Wrapper

  def start_link(_args) do
    GenServer.start_link(__MODULE__, %{}, name: __MODULE__)
  end

  def init(state) do
    {:ok, state, {:continue, :put_mapping}}
  end

  def handle_continue(:put_mapping, state) do
    mapping = %{
      "index_patterns" => ["game_play-*"]
    }

    config = Application.get_env(:search_flask, :elasticsearch_seeds, [])

    if Keyword.get(config, :enabled?, true) do
      Wrapper.create_template_mappings("game_play", mapping)
    end

    {:noreply, state}
  end
end

and I am trying to put to test using Req, in Wrapper, I am sending an HTTP request using Req. but it only works once when I delete _build/test folder after that it stops working

defmodule GamePlayTest do
  use ExUnit.Case, async: true

  alias GamePlay
  alias Wrapper

  describe "GamePlay" do
    setup do
      on_exit(fn ->
        Req.Test.verify_on_exit!()
      end)

      :ok
    end

    test "sends the correct request to Elasticsearch" do
      Req.Test.stub(Wrapper, fn conn ->
        Req.Test.json(
          conn,
          %{"acknowledged" => true}
        )
      end)

      assert {:ok, pid} = GamePlay.start_link(%{})

      assert %Req.Response{body: %{"acknowledged" => true}, status: 200} =
               Req.get!(Application.get_env(:search_flask, :elasticsearch_req_options, []))
    end
  end
end

I have this in test.exs as well.

config :search_flask,
  elasticsearch_req_options: [
    plug: {Req.Test, Wrapper}
  ]

the is the error.

     ** (EXIT from #PID<0.570.0>) an exception was raised:
         ** (RuntimeError) cannot find mock/stub Wrapper in process #PID<0.571.0>
             (req 0.5.6) lib/req/test.ex:399: Req.Test.__fetch_plug__/1
             (req 0.5.6) lib/req/test.ex:632: Req.Test.call/2
             (req 0.5.6) lib/req/steps.ex:927: Req.Steps.run_plug/1
             (req 0.5.6) lib/req/request.ex:1103: Req.Request.run_request/1
             (req 0.5.6) lib/req/request.ex:1047: Req.Request.run/1
             (search_flask 1.3.0) lib/game_play.ex:47: GamePlay.handle_continue/2
             (stdlib 6.0) gen_server.erl:2163: :gen_server.try_handle_continue/3
             (stdlib 6.0) gen_server.erl:2072: :gen_server.loop/7
             (stdlib 6.0) proc_lib.erl:329: :proc_lib.init_p_do_apply/3

the test is simple as well but it only reaches to Wrapper.create_template_mappings only once after that it just keep failing.