[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/downloading/media_download_worker_test.exs

@@ -1,7 +1,6 @@
 defmodule Pinchflat.Downloading.MediaDownloadWorkerTest do
   use Pinchflat.DataCase
 
-  import Mox
   import Pinchflat.MediaFixtures
 
   alias Pinchflat.Media
@@ -9,8 +8,6 @@ defmodule Pinchflat.Downloading.MediaDownloadWorkerTest do
   alias Pinchflat.Utils.FilesystemUtils
   alias Pinchflat.Downloading.MediaDownloadWorker
 
-  setup :verify_on_exit!
-
   setup do
     stub(UserScriptRunnerMock, :run, fn _event_type, _data -> :ok end)
     stub(HTTPClientMock, :get, fn _url, _headers, _opts -> {:ok, ""} end)