Issue 5383 - Add tests for the Chrome and Firefox packagers

tests/README.md

 # Buildtools unit tests
 
 ## Introduction
 
 Unit tests for buildtools, using the pytest framework.
 
 ## Approach
 
 In order to test the buildtools capability of creating WebExtension-packages
 for Chrome, Edge and Firefox, an example configuration for each platform is
 provided.
 Running the tests calls the same API as the cli would, except for releases
 (we don't want to trigger our releaseAutomation during tests) - in this case,
 a build is manually created and verified).
 
 Each extension is build with different parameters, the resulting package and
 it's content is compared against provided expected results:
 
 - Release or build-only, with or without a specific build-number (Edge)
 - Release, build-only or developement environment, with or without a specifc
   build-number (Chrome, Firefox), with or without a predefined signing key
   (Chrome)
 
 The expected results for each manifest are provided with the files in
 `expecteddata/`.
 
 ## Test cases
 
-_(Covered platforms are referred to as C=Chrome, E=Edge, F=Firefox)_
+_(Covered platforms are referred to as C=Chrome, E=Edge, F=Firefox.)_
 
 - Metadata inheritance (EF)
 - Correct package filename (CEF)
-- Printed warning about non-square icons (CF)
-- Presence of JavaScript unit test files in developement environment (CF)
-- Absence of JavaScript unit test files in build-only or release (CF)
-- Inlcusion of defined contentScripts into the manifest (CF)
+- Printed warning about non-square icons (CEF)
+- Presence of JavaScript unit test files in developement environment (CEF)
+- Absence of JavaScript unit test files in build-only or release (CEF)
+- Inlcusion of defined contentScripts into the manifest (CEF)
 - Packaging (and moving) of included icons / scripts / HTML files (CEF)
 - Presence of files for all configured locales (CEF)
 - Correct import of translations with or without placeholders, with or without
   access keys (CEF)
 - Translation presence and validity for the Chrome Web Store (C)
 - Packaging of modularized script files with webpack (CEF)
 - Adherence to provided build-number in the manifest (CEF)
 - Other content in the manifest (CEF)
 - Correct encrypted signature of the package (C)
 
@@ skipping 17 matching lines @@
 ## Coverage
 
 Pytest will create a coverage report as output to the terminal, using the
 pytest plugin `pytest-cov`.
 
 In order to get an html report you can add `--cov-report=html` to the
 pytest-command in tox.ini.
 
 For more information please refer to the
 [coverage documentation](https://coverage.readthedocs.io/)