Iox #521 best practice for testing

[elBoberido]

Pre-Review Checklist for the PR Author

1. Branch follows the naming format (iox-#123-this-is-a-branch)
2. Commits messages are according to this guideline
   • Commit messages have the issue ID (iox-#123 commit text)
   • Commit messages are signed (git commit -s)
   • Commit author matches Eclipse Contributor Agreement (and ECA is signed)
3. Update the PR title
   • Follow the same conventions as for commit messages
   • Link to the relevant issue
4. Relevant issues are linked
5. Add sensible notes for the reviewer
6. All checks have passed
7. Assign PR to reviewer

Notes for Reviewer

This PR tries to document the our best practices to write tests for iceoryx. Some of them were unwritten, making it hard for new contributor to write test the way we expect it.
I still have to write a small example for typed and parameterized test, but this will be more or less just a template for c&p and all the other stuff is done and can be reviewed.
Oh, and I fixed a typo from my last PR.

Checklist for the PR Reviewer

• Commits are properly organized and messages are according to the guideline
• Code according to our coding style and naming conventions
• Unit tests have been written for new behavior
• Public API changes are documented via doxygen
• Copyright owner are updated in the changed files
• PR title describes the changes

Post-review Checklist for the PR Author

1. All open points are addressed and tracked via issues

Post-review Checklist for the Eclipse Committer

1. All checkboxes in the PR checklist are checked or crossed out
2. Merge

References

• Partly closes Improve Pull-Request Process #521

[dkroenke]

There should be a link from https://github.com/eclipse-iceoryx/iceoryx/blob/master/CONTRIBUTING.md#testing to this document.