Python: Add tests to Purview Package

[Rishabh4275]

Motivation and Context

Add Tests for test coverage
Closes #3358

Description

Add Tests for test coverage. Increased test coverage from 84 to 89 percent.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull request overview

This PR extends the Purview Python package’s test suite to cover additional edge cases in the processor, middleware, client, and cache components, with a focus on payment-required behavior, correlation IDs, caching semantics, and error handling.

Changes:

• Added processor tests around corrupted cache entries, tenant-level payment-required exception caching, and background re-processing behavior when scopes are modified.
• Expanded middleware and chat middleware tests to cover streaming behavior, 402 Payment Required handling, and ignore_exceptions behavior in both pre- and post-check paths.
• Extended Purview client and cache tests to cover correlation ID propagation, 402 handling, deserialization failures, invalid JSON bodies, ContentActivities calls, and conservative cache size-estimation fallbacks.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
python/packages/purview/tests/test_processor.py	Adds tests for cache behavior (including corrupted entries), tenant-level payment-required caching, and background retry logic when protection scopes change.
python/packages/purview/tests/test_middleware.py	Adds agent middleware tests for streaming (post-check skip), 402 behavior, and exception propagation based on ignore_payment_required and ignore_exceptions.
python/packages/purview/tests/test_client.py	Extends client tests to cover ETag header precedence, 402 handling (both _post and process_content), correlation ID header/span behavior, deserialization-fallback paths, and content activities.
python/packages/purview/tests/test_chat_middleware.py	Adds chat middleware tests for 402 behavior and exception propagation in pre- and post-checks, mirroring agent middleware semantics.
python/packages/purview/tests/test_cache.py	Adds a test ensuring _estimate_size falls back to a conservative size when both JSON serialization and sys.getsizeof fail.

[markwallace-microsoft]

Python Test Coverage Report •

File	Stmts	Miss	Cover	Missing
packages/purview/agent_framework_purview
_processor.py	164	10	93%	160, 236–239, 244, 272, 274, 280, 282
TOTAL	16248	1982	87%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
3740	221 💤	0 ❌	0 🔥	1m 8s ⏱️