test(changes follower): cover zero limit edge case - #5

PR summary

Adds test_limit_zero to both TestChangesFollowerFinite and TestChangesFollowerListen, covering the boundary of the existing limits fixture (100, _BATCH_SIZE, _BATCH_SIZE + 123) which never exercises limit=0.

With limit=0 the follower takes a distinct path: _run clamps batch_size to 0 and _ChangesFollowerIterator.__next__ short-circuits on limit == 0 before consuming the buffer, so the iterator must stop cleanly (including joining the request thread) with zero changes even though the mocked feed has MAX_BATCHES available. In LISTEN mode this is the only condition under which the feed terminates on its own without stop() or an error.

Both tests use the shared runner with a generous timeout, so a regression that hangs (e.g. blocking on Queue.get) or emits changes fails the assertion rather than passing vacuously.

Fixes: n/a — test-only addition.

PR Checklist

Please make sure that your PR fulfills the following requirements:

• The commit message follows the
  Angular Commit Message Guidelines.
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• New tests
• Build/CI related changes
• Documentation content changes
• Other (please describe)

What is the current behavior?

limit=0 is untested in both operating modes.

What is the new behavior?

No production code changes; the zero-limit behaviour is now asserted for FINITE and LISTEN modes.

Does this PR introduce a breaking change?

• Yes
• No

Other information

python -m pytest test/unit/features/test_changes_follower.py (41 passed) and python -m pylint --rcfile=.pylintrc ibmcloudant (10.00/10) pass locally.

Link to Devin session: https://app.devin.ai/sessions/a8f6ece030764ec194d962c4552b83cf
Requested by: @eml2026