[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/source_controller_test.exs

@@ -1,6 +1,5 @@
 defmodule PinchflatWeb.SourceControllerTest do
   use PinchflatWeb.ConnCase
-  import Mox
 
   import Pinchflat.MediaFixtures
   import Pinchflat.SourcesFixtures
@@ -32,8 +31,6 @@ defmodule PinchflatWeb.SourceControllerTest do
     }
   end
 
-  setup :verify_on_exit!
-
   describe "index" do
     test "lists all sources", %{conn: conn} do
       conn = get(conn, ~p"/sources")