test: improve json parser test cases for json-iterator/go

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 93.52%. Comparing base (ea6c47e) to head (e0bf6f9).

:exclamation: Current head e0bf6f9 differs from pull request most recent head c1b66a6. Consider uploading reports for the commit c1b66a6 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #627 +/- ## ======================================= Coverage 93.52% 93.52% ======================================= Files 48 48 Lines 2518 2518 ======================================= Hits 2355 2355 Misses 106 106 Partials 57 57 ```

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