tests for the mss main() function

[ReimarBauer]

Purpose of PR?:

Fixes #659

Does this PR introduce a breaking change?

If the changes in this PR are manually verified, list down the scenarios covered::

Additional information for reviewer? : Mention if this PR is part of any design or a continuation of previous PRs

Does this PR results in some Documentation changes? If yes, include the list of Documentation changes

Checklist:

• [ ] Bug fix. Fixes #
• [ ] New feature (Non-API breaking changes that adds functionality)
• [ ] PR Title follows the convention of <type>: <subject>
• [X] Commit has unit tests

[ReimarBauer]

@matrss Looks like my changes are causing the timeout.