snapbox-testing

# Snapbox Testing Use this skill to make Rust command-output tests simpler, more stable, and easier to review. ## Follow This Workflow 1. Replace manual output plumbing with direct snapbox assertions. 2. Start from empty inline snapshots (`snapbox::str![""]`) for unstable/unknown output. 3. Run tests with `SNAPSHOTS=overwrite` to capture real output. 4. Tighten snapshots by keeping stable text exact and wildcarding only volatile parts. 5. Re-run tests and clippy. Use: ```bash SNAPSHOTS=overwrite cargo test -p <crate> --test <test-target> ``` ## Prefer These Patterns - Assert command result directly: - `.assert().success().stdout_eq(...)` - `.assert().failure().stderr_eq(...)` - Prefer inline snapshots: - `snapbox::str![[r#"...\n"#]]` for multi-line outputs - string literals for short exact lines - Keep assertions local and readable: - inline expected value when used once - avoid temporary `expected_*` bindings unless reused ## Minimize Redaction - Prefer built-in wildcard filters first: - `[..]` for variable substrings within a line - `...` on its own line for variable trailing frames/lines - Keep stable semantics visible: - preserve meaningful suffixes like `/_build/.../main.wasm` - avoid over-redacting fixed tokens (for example, exact error kind/message) - Add custom `Redactions` only when wildcard patterns cannot express the instability clearly. ## Cross-Platform Guidance - Rely on snapbox default path normalization before adding platform-specific `cfg` snapshots. - Use one snapshot when separator normalization is sufficient. - Add `cfg(windows)`/`cfg(not(windows))` split only for truly semantic OS differences. ## Avoid - Manual `.get_output().stdout/stderr` + UTF-8 parsing when direct assertions work. - Hand-written normalization helpers for paths/stack traces when snapbox patterns can express intent. - Broad wildcarding that hides behavior regressions. ## Quick Checklist - `cargo fmt --all` - `cargo test -p <crate> --test <target>` - `cargo clippy -p <crate> --tests -- -D warnings`