Improve forcetest (by Ian)

[ttarczynski]

Link issues resolved by this: Resolves #

Changes/added features:

• Allow to force tests for any single example

The following short checklist should be used to make sure your PR is of good quality, and can be merged easily:

• [x] follows project conventions
• [x] follows project principles
• [x] ./run.sh works correctly for all new examples
• [x] CI checks pass
• [x] mergeable to main (no conflicts)
• [x] resolved issues linked

Reviewers: @ianmiell @ttarczynski @sanyer

[ttarczynski]

@ianmiell I moved your changes to .forcetest here from integration. LGTM, I'll merge it.