Jon Chery
44 lines
1.3 KiB
Markdown
44 lines
1.3 KiB
Markdown
# Testing — First Principles
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## 1. The Principles
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### P1. Tests as Specification
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Tests document what the code should do. Reading the tests is reading
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the contract.
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### P2. Independence
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Tests do not depend on each other. Order does not matter. Parallelism
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is the default.
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### P3. Determinism
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Same input, same output, every time. No time, randomness, network, or
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filesystem in the test path unless explicitly modeled.
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### P4. Fast Feedback
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Tests run in seconds, not minutes. Slow tests are skipped, then
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deleted.
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### P5. Coverage of Behavior
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Cover what the code does, not what it is. Lines covered is not the
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goal. Behaviors exercised is the goal.
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### P6. Failure Specificity
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A failing test names the file, the function, the input, the
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expectation, and the actual. A test that fails unhelpfully is
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broken.
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### P7. Realism
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Test data resembles production data in shape, distribution, and
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edge cases. Toy data hides bugs.
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### P8. Maintainability
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Tests are first-class code. They are read, reviewed, and refactored.
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Test code is not throwaway.
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### P9. Edge Case Coverage
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Boundaries, nulls, empty sets, maximums, minimums, and invalid inputs
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are tested. The middle of the range is the easy part.
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### P10. No Test Theater
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A test that cannot fail is not a test. A test that asserts nothing
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is a lie. Tests earn their place by being able to catch real bugs. |