Experiment with testing web extension examples

[kumar303]

As a first step to understanding what the test command should do (#5), let's try and add tests to the web extension examples.

Things to try:

• See how far we can get by writing unit tests (e.g. run in Node with mocha) that completely stub out the web extension APIs. This strategy would trust the documented APIs and exercise the units of developer code that work with the APIs.
• Try shimming / mocking parts of the web extension API to test things like background scripts or message passing.

Here are more detailed notes from a brainstorming meeting about this https://docs.google.com/document/d/1fx27HyovxBlZ0M0kl3FZ0pJX7dOCgUlYF8tOKOWowus/edit#

[kumar303]

There is an example in progress here although it's a little cumbersome: mdn/webextensions-examples#130

[motin]

There is an example in progress here although it's a little cumbersome: mdn/webextensions-examples#130

Note that this example will probably be removed soon: mdn/webextensions-examples#398