Tests: ngx_http_json_module tests.

[roman-f5]

Proposed changes

Added json_parser.t covering json_set value extraction (scalars, nested
objects and arrays, compound containers, literals, number types, escapes,
the '$' root selector, source caching, last-match-wins on duplicate keys,
quoted key segments, and binary-safe / Unicode / surrogate-pair keys), and
json_parser_invalid.t covering rejection of malformed json_set paths at
configuration load.

Checklist

Before creating a PR, run through this checklist and mark each as complete:

• I have read the contributing guidelines.
• I have signed the F5 Contributor License Agreement (CLA).
• If applicable, I have added tests that prove my fix is effective or that my feature works.
• If applicable, I have checked that any relevant tests pass after adding my changes.
• I have updated any relevant documentation (README.md and/or CHANGELOG.md).

[dekobon]

The PR description no longer matches the diff: it says there is a separate json_parser_invalid.t file, but this PR only adds json_parser.t, and it lists $ root selector extraction even though the test correctly asserts that $ is rejected.

Could the description be updated to match the current coverage?

[pluknet]

please rename json_parset.t to json_set.t - to follow the naming convention of using the (main) directive name as exported by the tested module

I didn't look deeply into the essence of the tests, especially into the syntax-related.
If you believe they are truly needed and they pass on all tested platforms, I'm ok to keep them.

[route443]

It's time to take care of these tests a bit! Roman -> Ivan

[route443]

All of pluknet's comments are addressed.
Plus the coverage gaps and two defects in the config-check helper:

• tests added to cover whitespace characters (ngx_json_ws() branch)
• certain num vals ​​and exponent sign processing
• top-level scalars
• expanded malformed docs tests
• escape decoding
• empty string val
• some config time tests

Plus some issues with config checks:

• run_check_conf() writes the config using standard open/print calls, bypassing write_file_expand() => listen 127.0.0.1:8080 directive within it is not replaced with the allocated port => prove -j = fail
• server {} block is unnecessary and removed

Now we have 102 tests. Coverage:

file	strings	branches
ngx_http_json_module.c	92.33% (391)	82.05% (234)
ngx_json_parse.c	89.46% (408)	79.72% (355)
ngx_json_unescape.c	96.77% (124)	85.94% (64)

Delta relative to the previous coverage: +1.8 / +11.8 / +15.3 by line, +1.7 / +17.8 / +17.2 by branch.

I made a few adjustments to the sandbox CI so that the json module builds by default and there are no checks in has(). All tests are passing successfully.