FIX: Fixed bugs in existing test suite and added additional stress tests

[gargsaumya]

New tests:

• test_executemany_large_batch_mixed_types: 10k rows, mixed types via executemany
• test_null_heavy_large_result_set: 50k rows with 6/8 cols NULL, verify None propagation
• test_cursor_reuse_high_iteration: single cursor reused 5000 times, memory leak check
• test_fetchone_loop_vs_fetchall_parity: 100k row bit-identical comparison of both fetch paths
• test_concurrent_read_write_no_corruption: 5 writers + 5 readers on shared table for 10s

Bug fixes:

• test_concurrent_fetch_data_integrity_no_corruption: verification block was inside thread.join() loop instead of after it (race condition + premature fail)
• test_pool_exhaustion_recovery: pool max_size was silently overridden by run_parallel(); added pool_max_size param to MultiThreadedQueryRunner; fixed multi-statement query
• test numbering: docstring sequence skipped Update README #4 (renumbered Readme Updates -2 #5-Updated the heading of the page #7 -> Update README #4-Readment Updates - 3 #6)

Also registers 'slow' mark in pytest.ini to suppress PytestUnknownMarkWarning

Work Item / Issue Reference

AB#<WORK_ITEM_ID>

GitHub Issue: #<ISSUE_NUMBER>

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Summary

This pull request adds several new high-scale stress tests and improves the configurability and coverage of both single-threaded and multi-threaded stress testing. The main updates include three new single-threaded stress tests for executemany with mixed types, NULL-heavy result sets, and high-iteration cursor re-use, plus a fetchone vs fetchall parity test. Multi-threaded stress tests now support explicit pool size configuration and improved pool exhaustion testing. Test documentation and marker registration have also been updated.

Single-threaded stress test enhancements:

• Added test_executemany_large_batch_mixed_types to stress-test executemany() with 10,000 mixed-type rows, verifying parameter serialization and correctness.
• Added test_null_heavy_large_result_set to fetch 50,000 rows with 6/8 columns as NULL, ensuring correct NULL handling at scale.
• Added test_cursor_reuse_high_iteration to re-use a single cursor for 5,000 execute/fetch cycles, checking for memory leaks and state reset.
• Added test_fetchone_loop_vs_fetchall_parity to verify bit-identical results between fetchone() and fetchall() for 100,000 rows.
• Updated test docstrings and numbering for clarity and completeness. [1] [2] [3] [4]

Multi-threaded stress test improvements:

• The MultiThreadedQueryRunner now accepts a pool_max_size parameter, allowing explicit control of the connection pool size in tests. [1] [2]
• The pool exhaustion test (test_pool_exhaustion_recovery) now uses the explicit pool size parameter and improved query logic for more accurate stress simulation and reporting. [1] [2]
• Test documentation updated to clarify coverage of pool exhaustion and concurrent mixed read/write.

Test marker and config updates:

• Registered a new slow pytest marker for extra-slow tests, complementing the existing stress marker.

These changes expand test coverage for edge-case and high-load scenarios, improve test documentation, and make stress tests more configurable and robust.

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

This PR expands the stress test suite with additional high-scale single-threaded and multi-threaded scenarios, and fixes a few correctness/config issues in existing tests.

Changes:

• Added multiple new single-threaded stress tests (executemany mixed types, NULL-heavy results, cursor reuse, fetch parity).
• Improved multi-threaded stress runner configurability via explicit pool_max_size, and updated pool exhaustion test accordingly.
• Added a new concurrent mixed read/write stress test and registered the slow pytest marker.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 7 comments.

File	Description
tests/test_020_multithreaded_stress.py	Adds pool_max_size to the runner, adjusts pool exhaustion test, and introduces a new concurrent read/write stress test.
tests/test_011_singlethreaded_stress.py	Fixes a race in existing concurrent fetch verification and adds several new large-scale stress tests.
pytest.ini	Registers the slow marker to avoid unknown-mark warnings.

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[github-actions]

📊 Code Coverage Report

🔥 Diff Coverage 100%

🎯 Overall Coverage 79%

📈 Total Lines Covered: 6677 out of 8449 📁 Project: mssql-python

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Diff Coverage

Diff: main...HEAD, staged and unstaged changes

No lines with coverage information in this diff.

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📋 Files Needing Attention

📉 Files with overall lowest coverage (click to expand)

mssql_python.pybind.logger_bridge.cpp: 59.2%
mssql_python.pybind.ddbc_bindings.h: 67.8%
mssql_python.row.py: 70.5%
mssql_python.pybind.logger_bridge.hpp: 70.8%
mssql_python.pybind.ddbc_bindings.cpp: 74.2%
mssql_python.pybind.connection.connection.cpp: 75.8%
mssql_python.__init__.py: 77.3%
mssql_python.ddbc_bindings.py: 79.6%
mssql_python.pybind.connection.connection_pool.cpp: 79.6%
mssql_python.connection.py: 85.2%

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