Git basics
Instrument the focused Git commit
Page 6 adds signals that distinguish bad input from component failure in the focused commit for evaluation-script change.
1Learn the idea
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Emit stage signals
Instrument the focused commit for evaluation-script change so a run records enough structure to debug offline: counts, latency if relevant, pass/fail of git diff --cached --name-only shows only train.py before commit, and a stable stage name. Redact secrets and raw credentials from every event.
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Emit and assert
git log -1 --pretty=format:'%h %s' ; echo; git show --name-only --pretty='' HEAD
Expected evidence: hash, subject, file list. Prefer JSON or structured text you can grep in CI over prose logs for git-basics.
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Lock signals with a regression test
Turn one historical failure—especially accidentally staging both files—into a test that fails if the signal disappears for the focused Git commit. Observability without a failing test is optional decoration; observability with a test is part of the git-basics artifact.
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Lab notebook: signal schema
Draft a three-field event for the focused Git commit: stage, ok, and one domain field derived from git diff --cached --name-only shows only train.py before commit. Add fixture_id or docs_version when content can change. Explicitly list fields that must never appear (tokens, passwords, raw prompts) because staging a .env or credentials file beside the evaluation change is in scope for this lab.
Wire one assertion that fails if the focused Git commit event is missing after a run. Observability that cannot fail a test will not survive contact with a busy git-basics repository.
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Worked judgment
Imagine a teammate opens only your event stream after a bad deploy. Could they tell whether repo with dirty train.py (eval) and README.md (docs) was wrong, whether accidentally staging both files, or committing from the wrong directory returned, or whether staging a .env or credentials file beside the evaluation change slipped through? If not, rename fields until those three stories are distinguishable.
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Why this stage matters for the focused Git commit
At the testing and observability stage for git-basics, the job is narrower than finishing a product demo. You are creating one progressive evidence piece about repo with dirty train.py (eval) and README.md (docs) that later pages inherit without redefining success. Keep that fixture small enough to inspect by hand, keep outputs copy-pasteable as text, and refuse to narrate this baseline as if it were a production SLA: git status and git diff before any add.
For this page specifically, success looks like a structured event schema locked by a test while still centering the user decision to land only the tested train.py evaluation change while README edits stay unstaged. If you cannot point to a file, command, or assertion that proves that for the focused Git commit, stay on this page instead of advancing.
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Before you start
Why this matters
Write the single log line or metric event that would tell you whether a bad result came from input vs implementation for the focused Git commit. If your line could not tell them apart, redesign it before coding.
In the wild
See how this idea shows up as a product and a company — then come back to the lesson. Skills transfer across vendors.
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