Improve Mock module to work properly with Timeout middleware (#668)

Co-authored-by: Yordis Prieto <[email protected]>

lib/tesla/mock.ex

@@ -226,7 +226,16 @@ defmodule Tesla.Mock do
   end
 
   defp pdict_set(fun), do: Process.put(__MODULE__, fun)
-  defp pdict_get, do: Process.get(__MODULE__)
+
+  # Gets the mock fun for the current process or its ancestors
+  defp pdict_get do
+    pid_holder =
+      Enum.find(Process.get(:"$ancestors", []), self(), fn ancestor ->
+        !is_nil(Process.get(ancestor, __MODULE__))
+      end)
+
+    pid_holder |> Process.info() |> Keyword.get(:dictionary) |> Keyword.get(__MODULE__)
+  end
 
   defp agent_set(fun) do
     case Process.whereis(__MODULE__) do

test/tesla/mock_test.exs

@@ -84,6 +84,17 @@ defmodule Tesla.MockTest do
       assert env.status == 201
       assert env.body == %{"id" => 42}
     end
+
+    test "mock a request inside a spawned process" do
+      task =
+        Task.async(fn ->
+          assert {:ok, %Tesla.Env{} = env} = Client.get("/json")
+          assert env.status == 200
+          assert env.body == %{"json" => 123}
+        end)
+
+      Task.await(task)
+    end
   end
 
   describe "without mock" do