py2ml: `test_mockup.py` (4)

Context

Related to #3632 (closed).

Builds on !6435 (merged).

More translated mockup tests.

For info, python code is inlined with tezt code in the MR. Then, they are removed in fixup commits. If you want to review with python inlined, review commit by commit. If you prefer not seeing any python, review the full diff.

Manually testing the MR

tezt -f mockup.ml

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR