feat: prevent global mode in async tests (#110)

Similar to what Mox does, prevent this footgun by raising an exception

Co-authored-by: Riccardo Binetti <riccardo.binetti@remote.com>

Author: rbino

lib/mimic.ex

@@ -459,7 +459,14 @@ defmodule Mimic do
   ```
   """
   @spec set_mimic_global(map()) :: :ok
-  def set_mimic_global(_context \\ %{}), do: Server.set_global_mode(self())
+  def set_mimic_global(_context \\ %{})
+
+  def set_mimic_global(%{async: true}) do
+    raise "Mimic cannot be set to global mode when the ExUnit case is async. " <>
+            "If you want to use Mimic in global mode, remove \"async: true\" when using ExUnit.Case"
+  end
+
+  def set_mimic_global(_context), do: Server.set_global_mode(self())
 
   @doc """
   Chooses the mode based on ExUnit context. If `async` is `true` then

test/mimic_test.exs

@@ -1280,4 +1280,11 @@ defmodule Mimic.Test do
       end
     end
   end
+
+  describe "set_mimic_global/1" do
+    test "raises if the test case is async" do
+      message = ~r/Mimic cannot be set to global mode when the ExUnit case is async/
+      assert_raise RuntimeError, message, fn -> set_mimic_global(%{async: true}) end
+    end
+  end
 end