[dmccoystephenson]

Summary

Stage B (unit-test expansion) of the per-installation ID code in TraceClient.install_id_from_file and the constructor's install_id= handling. These are characterization tests only. No production code is changed.

• test_install_id_from_file_takes_an_id_of_exactly_the_tag_length_limit: a line of exactly MAX_TAG_LENGTH characters is accepted as the ID. Until now only the over-limit side (256) was tested. Lines with characters outside [A-Za-z0-9_.-] (a slash, an inner space) are skipped, and a file that already holds an ID is not rewritten.
• test_install_id_file_failures_are_logged_at_debug_only: both failure branches (could not read, could not write) log one [trace]-prefixed record each, and nothing above DEBUG. To reach the write branch, os.makedirs is made to fail with a mock for a file that does not exist.
• test_explicit_install_id_is_sent_as_given_without_the_files_character_rule: an ID passed as install_id= is only trimmed and length-checked. It is not held to the file's character rule, which matches the constructor docstring and the README.

Observation (not changed here)

test_unwritable_install_id_file_yields_an_in_memory_id_and_never_raises puts the ID path under a regular file. That path fails on the read (NotADirectoryError), not the write, so the "could not write" branch is not what it exercises. The outcome it asserts (an in-memory ID, nothing created) holds either way, and the new log test now covers the write branch directly. The test's name could be tightened in a later cycle.

Deferred

• The version tag is added even when it pushes an event past MAX_TAGS #16 is left open. It still needs an owner decision on whether the README promise that tags "always holds at least version" holds at the MAX_TAGS cap, and the change needs to land in step with trace-client-java (see the comments on the issue).

Java parity

No Java-visible behavior changed (tests only).

Test plan

• python3 -m unittest -v on Python 3.8.10 locally: Ran 67 tests, OK
• CI Build: test (3.8), test (3.10), test (3.12)

No tracking issue. The gap was found during triage.

This PR description was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

🤖 Generated with Claude Code

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drafted by Claude on behalf of Daniel Stephenson

[dmccoystephenson]

Self-review rubric (Phase 4), scored against the diff and CI on head bdc37c1:

• Scope: PASS. git diff origin/main --name-only lists only tests/test_trace_client.py (+30 lines, all test code).
• Tests-new: PASS (N/A). No new public names; three tests were added for existing behavior.
• Tests-fix: N/A. Characterization only, no production fix to revert.
• Sibling structure: PASS. The tests sit in the existing per-installation-ID section of TraceClientTest, reuse _tmpdir/_sent_tags/self.log, and use long plain-words names.
• Sibling renames: N/A. Nothing was renamed.
• Docs: PASS. No behavior changed. The new tests assert what the install_id_from_file docstring and the README "Where it lives" section already say (first valid line, at most 255 characters, never overwrites, never raises).
• Issue resolution: N/A. No Closes. The gap was found during triage, and The version tag is added even when it pushes an event past MAX_TAGS #16's deferral is recorded in the PR body.
• CI: PASS. test (3.8), test (3.10) and test (3.12) are green on the PR head.
• Stdlib-only: PASS. git diff origin/main | grep -c '^+.*import' gives 0, and pyproject.toml is untouched.
• Py3.8 floor: PASS. test (3.8) is green, and the local run on 3.8.10 also passed (Ran 67 tests, OK).
• Never-raises / never-blocks: N/A. No production code changed.
• Log level: PASS. No _LOG. lines were added. The new test asserts that both install-ID failure paths log only at DEBUG.
• Version agreement: PASS. No version string was touched.
• Exports: N/A. No new public names.
• Java parity noted: PASS. The PR body says no Java-visible behavior changed.

Judgment calls:

• tests/test_trace_client.py:719 — mock.patch("trace_client.trace_client.os.makedirs", ...) patches the shared os module's attribute, so the patch applies process-wide while the with block runs. Nothing else calls os.makedirs during that window (no sender thread is alive in this test), so it is safe as written. A future test that runs work concurrently inside such a block would need to scope it more narrowly.
• The existing test_unwritable_install_id_file_yields_an_in_memory_id_and_never_raises exercises the read-failure branch, not the write-failure branch (this is described in the PR body). Its assertions still hold. A rename is left for a later cycle so that this PR stays additive.

Summary: tests-only, additive, CI green on all three interpreters, and no do-not-auto-merge path is touched.

This review comment was drafted during a Gardener session (https://github.com/Stephenson-Software/gardener).

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drafted by Claude on behalf of Daniel Stephenson