Add basic test for Records.Cover module

lib/music_library/records/cover.ex

@@ -1,5 +1,6 @@
 defmodule MusicLibrary.Records.Cover do
   @size 600
+
   def resize(cover_data) do
     {:ok, thumb} = Vix.Vips.Operation.thumbnail_buffer(cover_data, @size)
     Vix.Vips.Image.write_to_buffer(thumb, ".jpg")

test/music_library/records/cover_test.exs

@@ -0,0 +1,14 @@
+defmodule MusicLibrary.Records.CoverTest do
+  use ExUnit.Case, async: true
+
+  import MusicLibrary.RecordsFixtures
+
+  describe "resize/1" do
+    test "it resizes to the desired size" do
+      cover_data = File.read!(marbles_cover_fixture())
+      {:ok, resized_cover} = MusicLibrary.Records.Cover.resize(cover_data)
+      assert cover_data !== resized_cover
+      assert MusicLibrary.Records.Cover.correct_size?(resized_cover)
+    end
+  end
+end