[Feat] Add full test coverage for --json parameter

[wenzeslaus]

The standard option for generating JSON version of the command line parameters, the --json parameter, has basic functionality covered in tests. The tests were added in #6310 which states that not all cases are covered.

New tests should be added or existing modified to achieve full test coverage of the --json code.

A PR for this should include a reproducible analysis of what was missing and what/why the new tests cover it.

[saurabh12nxf]

Hi @wenzeslaus
I noticed the note in #6310 mentioning that the existing tests don’t cover all cases handled in the code or described in the comments.
Before proposing any changes, I’ll go through the current test coverage and compare it with the implementation in parser_json.c to identify the specific gaps.
I’ll come back with a good implementation plan
which code paths are already covered,
which scenarios are currently missing,
and what additional tests would be needed to reach full coverage.

This may take a bit of time since I want to do it carefully and make sure the analysis is solid.

[echoix]

Test coverage isn't collected for C tools in CI, neither for Python code ran by gunittest, and has some limits in pytest.

(Gcov has a too big impact, and by using source based llvm coverage, I didn't get to have a reliable collection of results when doing the full run)

[wenzeslaus]

Right @echoix, an analysis of the code is needed...unfortunately.

[sakirr05]

@wenzeslaus I've reviewed the code in lib/gis/parser_json.c and the existing tests.

main gaps:
->Multiple flags (only single-flag tested)
-> Mapset-only input (mapset stripping path)
->Vector export and file import scenarios
-> \f and \b escape sequences
Also found that test_json_escape_vector_output_parameter appears to assert on result["inputs"]["map"] when it should check result["outputs"]["output"] for v.random output=....