snapbox-testing - SKILL.md Agent Skill

name: snapbox-testing description: Write and maintain Rust CLI/integration tests with snapbox 0.6+ using command assertions, inline snapshots, and minimal wildcard/redaction patterns. Use when replacing manual `get_output` parsing, stabilizing cross-platform snapshots, or refining existing snapbox assertions.

Use this skill to make Rust command-output tests simpler, more stable, and easier to review.

Replace manual output plumbing with direct snapbox assertions.
Start from empty inline snapshots (snapbox::str![""]) for unstable/unknown output.
Run tests with SNAPSHOTS=overwrite to capture real output.
Tighten snapshots by keeping stable text exact and wildcarding only volatile parts.
Re-run tests and clippy.

Use:

SNAPSHOTS=overwrite cargo test -p <crate> --test <test-target>

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

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.

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.

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.