[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/fast_indexing/fast_indexing_worker_test.exs

@@ -1,15 +1,12 @@
 defmodule Pinchflat.FastIndexing.FastIndexingWorkerTest do
   use Pinchflat.DataCase
 
-  import Mox
   import Pinchflat.SourcesFixtures
 
   alias Pinchflat.Settings
   alias Pinchflat.Sources.Source
   alias Pinchflat.FastIndexing.FastIndexingWorker
 
-  setup :verify_on_exit!
-
   describe "kickoff_with_task/2" do
     test "starts the worker" do
       source = source_fixture(fast_index: true)