Formatter: JUnit

[ryandcoates]

User story.
As a cli user, I can do output in a format supported by Azure Pipelines, so that I can display the test report during each pipeline run.

Describe the solution you'd like
Azure piplines 'Publish Test results' task supports a number of outputs, assume JUnit or NUnit/XUnit would be the best option
More info here

[philsturgeon]

JUnit would definitely be useful, for Azure, CircleCI, and most other popular tools. It’s the one I’ve needed the most. https://circleci.com/blog/how-to-output-junit-tests-through-circleci-2-0-for-expanded-insights/

I assume with that done we can add other similar formats like xUnit in the future.

For junit implementation, I’d suggest using ESLint as inspiration. https://eslint.org/docs/user-guide/formatters/#junit