[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/metadata/metadata_file_helpers_test.exs

@@ -1,6 +1,6 @@
 defmodule Pinchflat.Metadata.MetadataFileHelpersTest do
   use Pinchflat.DataCase
-  import Mox
+
   import Pinchflat.MediaFixtures
 
   alias Pinchflat.Metadata.MetadataFileHelpers, as: Helpers
@@ -11,8 +11,6 @@ defmodule Pinchflat.Metadata.MetadataFileHelpersTest do
     {:ok, %{media_item: media_item}}
   end
 
-  setup :verify_on_exit!
-
   describe "compress_and_store_metadata_for/2" do
     test "returns the filepath", %{media_item: media_item} do
       metadata_map = %{"foo" => "bar"}