Issue 5383 - Add tests for the Chrome and Firefox packagers

tests/test_packagerEdge.py

 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+import xml.etree.ElementTree as ET
+
 import pytest
-
-import xml.etree.ElementTree as ET
 
 from buildtools import packager, packagerEdge
 
 
 @pytest.fixture
 def files():
     """Minimal Files() for testing blockmap."""
     str500 = b''.join(chr(i % 200 + 30) for i in range(500))
     files = packager.Files(set(), set())
     files['Extension/foo.xml'] = str500
@@ skipping 60 matching lines @@
         'js': 'application/javascript',
         'json': 'application/json',
         'otf': 'application/octet-stream',
         'png': 'image/png',
         'xml': 'application/xml'
     }
     assert ctm_dict['overrides'] == {
         '/AppxBlockMap.xml': 'application/vnd.ms-appx.blockmap+xml',
         '/AppxManifest.xml': 'application/vnd.ms-appx.manifest+xml'
     }