Add unit tests for query value operators

Values passed in queries can have operators e.g. `__gt` for comparison or to specify the type to use e.g. `__int`. We should add unit tests to cover the logic involved in order to detect any regression if the implementation changes.

No file or existing test is named. Start by locating the query value operator handling and the current unit-test structure; add coverage for comparison operators such as __gt and type operators such as __int, then run the relevant unit-test suite to verify regression coverage.

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