test(sensors): cover TracingSensor (distributed_tracing) 0% → 100%

[wbarnha]

What

Adds a unit-test suite for faust/sensors/distributed_tracing.py, which had no tests at all (0% coverage — the single largest testable coverage gap on master).

Coverage

faust/sensors/distributed_tracing.py: 0% → 100% (all 102 statements and all 30 branches). That's the biggest single-module coverage win available without new dependencies.

Tests (tests/unit/sensors/test_distributed_tracing.py, 24 cases)

Exercises every TracingSensor callback and both sides of each branch, driving the opentracing tracer/spans through mocks:

• app_tracer / kafka_tracer cached properties
• on_message_in — with trace-context headers (extract + follows_from) and without
• on_stream_event_in — parent span present/absent; stream_meta and stream_spans created fresh vs. reused
• on_stream_event_out — span finished/popped, no-spans, and stream-not-present
• on_message_out — span present/absent
• on_send_initiated — parent span present/absent
• on_send_completed — span present/absent
• on_send_error — error tag + log_kv + finish(exception=…), and no-span
• trace_inject_headers — success, no-tracer, no-span, and the exception→None path
• stop — closes aiohttp sessions, and the no-sessions path
• on_threaded_producer_buffer_processed

Notes

• Test-only change; no source touched.
• The other two 0%-coverage modules aren't covered here because they need optional deps this environment/CI doesn't install: faust/contrib/sentry.py (needs raven/sentry_sdk) and faust/stores/aerospike.py (needs the aerospike client). Those are worth a follow-up once their extras are added to the test matrix.
• Verified locally: 24 passed; flake8/black clean. (Pre-existing, unrelated test_datadog.py collection errors in this environment are a local datadog-dep issue, not affected by this change.)

🤖 Generated with Claude Code

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Generated by Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.02%. Comparing base (5bf3405) to head (456a668).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #733      +/-   ##
==========================================
+ Coverage   95.11%   96.02%   +0.91%     
==========================================
  Files         104      104              
  Lines       11169    11169              
  Branches     1206     1206              
==========================================
+ Hits        10623    10725     +102     
+ Misses        452      350     -102     
  Partials       94       94              

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