Introduce reporting code coverage for our repositories

[aliuk2012]

I noticed that we are do not have any form of test coverage reporting implemented as of yet. We will never be able to get to 100% coverage (and thats OK) but it does indicate to ourselves and future devs what state our code/tests are in and should give us confidence that we are testing everything in the right way.

I would like to propose that we use sonarcloud.io to provide code coverage for us. I have used codeclimate before in the past but found sonarcloud to provide a modern UI that integrates well with Github. As you will see for the screenshot below, it doesn't just coverage Ruby on Rails but also JavaScript testing too. Another neat feature is also keeping an eye on security issues that we might introduce or even pushing up invalid HTML.

GDS already use it for a few repositories

Other departments also use it as an example of where its being used and one randomly selected repository showing their status

Once its been integrated into the repo every PR will have this sort of comment added to them

At the moment we wouldn't block branches being merged and it would be used purely as a means to help improve quality and be consistent but later on once we are more confident with the test coverages we can start enforcing specific thresholds.

Any thoughts/ideas about taking this forward?

[aliuk2012]

Based on the 4 👍 we will be moving this forward