Do not include test folder in coverage report

What does this merge request do and why?

Exclude tests code from code coverage check. Before this MR, code coverage includes test code which result in incorrect percentage and coverage visualisation in MRs.

• Test coverage before: 81%
• Test coverage after: 70%

How to set up and validate locally

1. Check out to this merge request's branch.
2. Run the following command to run test coverage.

   make test-coverage

3. Confirm that there are not test files are in the coverage section.

Merge request checklist

• I've ran the affected pipeline(s) to validate that nothing is broken.
• Tests added for new functionality. If not, please raise an issue to follow up.
• Documentation added/updated, if needed.

Closes #207 (closed)