Add linting and testing to pipeline

about: Short explanation 🔧

We want to add linting and testing to the CI/CD pipeline.

What is the expected behaviour?

see above.

What is the actual behaviour?

no linting nor testing

Steps to Reproduce

Create a merge request.

Tasks

Include specific tasks in the order they need to be done in. Include links to specific lines of code where the task should happen at.

• add linting to changed files on an MR
• run tests when creating an MR

Any possible solutions?

Edit .gitlab-ci.yml