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rust-write-tests

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Expert-level Rust testing — the "What Could Break?" framework, five transformations from superficial to expert tests, flake hunting protocol, intent-based assertions, naming conventions, and a mandatory self-review checklist. Triggers on writing Rust tests, designing test cases, improving test quality, or reviewing test coverage.

skills/.curated/rust-write-tests/SKILL.md

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# Rust Test Writing Skill

Write tests that catch real bugs. Every test must guard a specific invariant -- not just prove the code "works."

## The "What Could Break?" Framework

Before writing any test, answer these four questions:

1. **What invariant does this code maintain?** (e.g., "deserialized config always has a default profile")
2. **What edge case would violate it?** (e.g., "empty TOML table, missing key, extra unknown key")
3. **What platform difference could surface?** (e.g., "path separators, case sensitivity, symlink behavior")
4. **What would a future refactor accidentally break?** (e.g., "field added to struct but not to Display impl")

If you can only answer #1, your test is a happy-path test. Answer all four and you have a regression suite.