Consider modification of file stream during Broccoli build rather than insertIntoFile() calls

[notmessenger]

Research modifying the Broccoli file stream rather than making actual physical changes to the files as currently doing in the blueprint. This will make it easier to swap test libraries in the future.

Since is "just" testing code the change can be applied on the fly and not have to be captured in source control. The source control change will be the inclusion of the addon in package.json

That's my current thinking anyways. Need to spend some more time with the idea

[notmessenger]

If modify the stream versus the on-disk file though it will be harder for the user to know when the add on was not able to successfully inject itself in the correct location in the files. This add on could keep up with Ember CLI version upgrades and the structures of the files but if a user has made enough changes to their application's copy of these files then the required injections will not occur properly. Would need to find a way to address this if using this approach.

[notmessenger]

Will likely be addressed by #159

[notmessenger]

Is this of any inspiration? ember-cli/ember-cli#2748

[notmessenger]

This should be done via blueprints instead of the need to write to files in this manner.