This topic presents who to setup kcov with cargo to get a test coverage for a cargo project, so I just assume you got kcov working in your Linux distribution and you have a project with source code and tests that you can run. I also assume you have gitlab-ci-multi-runner installed. So I will just quickly present who to configure it to use with GitLab CI to get test coverage badge in your new project.
I use my own CI runner, I’m not using shared runners or docker for it. So it’s pretty straightforward, your configuration will differ a bit.