SE401 · Annotated SlidesCode Coverage — Code Coverage
Code Coverage · Annotated slides

Code Coverage

What code coverage measures, its benefits and its false sense of security, best practices, and Google’s code-coverage best practices (60/75/90% guidelines, coverage of changed code, gating deployments).

Slide text Study notes Highlight: key words Tips, tricks & traps Seen again elsewhere How it can come up
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      1. Code coverage: the percentage of code (statements, branches, functions, lines) executed by the test suite.
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      1. Coverage finds UNTESTED code; it does not prove the tested code is correct: high coverage can give a false sense of security.
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      High code coverage guarantees high-quality tests.

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      1. Benefit: pinpoints which files and branches lack tests, guiding where to write more.
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          1. Coverage ≠ quality-tested code; a coverage target must not replace code review.
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          1. Write tests from the specification first, then use coverage to see what you missed.
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                            1. Google guideline: 60% acceptable, 75% commendable, 90% exemplary (no single "ideal" number).
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                            MCQ

                            Google’s guideline calls 75% code coverage:

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                                  1. Make sure frequently changing code is covered (per-commit coverage goals).
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                                    1. Gate deployments on coverage carefully: thresholds can become a checkbox that encourages bad tests.
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