fix(test): fix anthropic stream test mock missing get_final_message

[agent-of-mkmeral]

Problem

After #2047 introduced stream.get_final_message() in the Anthropic provider, the test_stream_message_stop_no_pydantic_warnings unit test started failing on Python 3.14 (failing run).

The test was manually constructing an async_generator as the stream mock via the agenerator fixture, which lacks the get_final_message() method. On Python 3.14, the async with context manager mock resolves differently, exposing this gap and causing:

AttributeError: 'async_generator' object has no attribute 'get_final_message'

Solution

Switched the test to use the existing generate_mock_stream_context helper, which properly creates a mock stream object with get_final_message support. This is consistent with how all other stream tests in the file are structured.

Related Issues

• Root cause: fix: handle premature stream termination for Anthropic (#1868) #2047
• Original issue fixed by fix: handle premature stream termination for Anthropic (#1868) #2047: [BUG] AttributeError on event.message.usage when Anthropic stream terminates before message_stop #1868

Type of Change

Bug fix (test)

Testing

• Verified the test passes locally on Python 3.12
• The fix uses the same generate_mock_stream_context helper used by all other stream tests in the file

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[gautamsirdeshmukh]

/strands review

[github-actions]

Assessment: Approve

Clean, minimal fix that correctly aligns this test with the established mocking pattern used by all other stream tests in the file. The switch from a raw async_generator mock to generate_mock_stream_context properly provides get_final_message() support, and the final_message construction with usage.model_dump is consistent with the other tests (e.g., test_stream, test_stream_structured_output).

No issues found — LGTM.