[Housekeeping] Improve test stability (#232)

* Ensured all tests use at least the DataCase module

* addressed one flakey test

* More flakey tests

* Consolidated Mox usage

test/pinchflat_web/controllers/media_item_controller_test.exs

@@ -1,14 +1,11 @@
 defmodule PinchflatWeb.MediaItemControllerTest do
   use PinchflatWeb.ConnCase
 
-  import Mox
   import Pinchflat.MediaFixtures
 
   alias Pinchflat.Repo
   alias Pinchflat.Downloading.MediaDownloadWorker
 
-  setup :verify_on_exit!
-
   describe "show media" do
     setup [:create_media_item]