Script that generates extracted coverage data from a replay

[markerikson]

Jest's coverage info can be written out in several formats (apparently based on Istanbul reporters).

It would be really neat if we had a Node script that could leverage the protocol API to:

• Log in and open up a recording by ID
• Extract all the sourcemapped file contents and line hit info
• Write that to disk in a format compatible with Istanbul, including generating the HTML file output that lets you view coverage in a browser

[markerikson]

This now exists! Mostly!

After posting this idea last night, today I was able to whip up a real live working example in just a few hours. It can successfully connect to our backend via the protocol API, fetch sources for a file, fetch line hits, and then uses the Istanbul code coverage tool's library APIs to generate a real HTML code coverage report!

It's still a proof-of-concept in that it's hardcoded to load one known recording and one specific file, but this proves out the basic principle.

From here, we could expand on this. Imagine showing code coverage percentages in the sources tree in our UI, or a button to export code coverage reports for download.

I've also created a new Replay protocol examples repo, and added both the code coverage script and Jason's React component stack frame analysis example:

https://github.com/RecordReplay/replay-protocol-examples