It would be useful if `libtest` would write a file in a format supported by CI systems. Based on [AppVeyor](https://www.appveyor.com/docs/running-tests/#uploading-xml-test-results) and [VSTS](https://docs.microsoft.com/en-us/vsts/pipelines/tasks/test/publish-test-results?view=vsts), it looks like `junit` or `xunit3` could be good choices.
