Page 4 of 8~112 min topic

Git basics

Measure whether the focused Git commit works

Page 4 turns “it ran” into executable checks for the focused commit for evaluation-script change.

~14 min this pageEvaluation

1Learn the idea

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Make the metric executable

Translate the claim into assertions or a tiny eval harness. The metric to protect is: git diff --cached --name-only shows only train.py before commit. Always record the denominator (how many cases) beside any rate. A percentage without a denominator is marketing, not measurement.

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Run the checks

git show --stat --name-only HEAD
git status --short  # README still dirty

Expected evidence: HEAD has train.py; README unstaged. A passing assertion proves only the behavior it names; broader usefulness still needs the chapter’s full limits.

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Say what the metric does not prove

Be explicit: beating the baseline (git status and git diff before any add) on this fixture does not prove behavior under accidentally staging both files, or committing from the wrong directory. Label observations separately from conclusions so the next page inherits honest evidence about the focused Git commit.

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Lab notebook: denominator discipline

Compute git diff --cached --name-only shows only train.py before commit with the denominator written beside the rate every time. For this chapter, the evaluation set is intentionally tiny; that is allowed only if you say so in the evidence. Compare against git status and git diff before any add before celebrating.

Add one negative case aimed at accidentally staging both files, or committing from the wrong directory. A suite with only happy cases cannot protect the focused Git commit when the characteristic failure appears in review.

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Worked judgment

If a check is expensive or flaky, shrink it until it is deterministic on repo with dirty train.py (eval) and README.md (docs). Flaky green builds teach the team to ignore gates. Record what this page does not prove so security-ops and mastery-ship inherit honest limits.

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Why this stage matters for the focused Git commit

At the evaluation 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 metrics with explicit denominators and a negative case 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.

Git glossary

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Extra mastery block

For git-basics, write a transfer example that differs in one constraint from the chapter scenario. Keep the quality bar fixed. Explain which check still applies.

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Extra mastery block

For git-basics, write a transfer example that differs in one constraint from the chapter scenario. Keep the quality bar fixed. Explain which check still applies.

Read

Extra mastery block

For git-basics, write a transfer example that differs in one constraint from the chapter scenario. Keep the quality bar fixed. Explain which check still applies.

Read

Extra mastery block

For git-basics, write a transfer example that differs in one constraint from the chapter scenario. Keep the quality bar fixed. Explain which check still applies.

Go deeper

Before you start

Why this matters

Write one independent check that would catch a fake pass for this lab. Prefer a check tied to git diff --cached --name-only shows only train.py before commit over a check that only asserts “no exception.”

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.

Check your understanding

Page assessment

Answer from memory. Completion is saved from this evidence, not from opening the next page.

1. Is the metric computed with an explicit denominator?
2. Does a failing gold case actually fail the harness?
3. Did you separate observations from conclusions?
4. What remains unproved after these checks?

All responses are required.