[KuSh]

Problem

Some tests assert against the machine they run on rather than against RTK.

Hard failure. test_git_status_not_a_repo_exits_nonzero matches git's English not a git repository on stderr. git status is a passthrough, so its message stays in the user's language by design (see git_cmd_c_locale's doc) — the test fails for anyone whose git speaks another language:

$ cargo test --all -- --ignored          # fr_FR.UTF-8
test cmds::git::git::tests::test_git_status_not_a_repo_exits_nonzero ... FAILED
$ LC_ALL=C cargo test --all -- --ignored
ok

Silent weakening, which is worse. search_faithful_test.rs asserts !out.contains("Is a directory") to prove rtk grep reads piped stdin instead of injecting a path. Wherever grep speaks another language the string can never appear, so the assertion passes without testing anything:

$ rtk grep pattern somedir
/usr/bin/grep: somedir: est un dossier          # negative assertion passes vacuously
$ LC_ALL=C rtk grep pattern somedir
/usr/bin/grep: somedir: Is a directory          # what the test was written against

Ambient repository. test_branch_creation_not_swallowed and test_branch_creation_from_commit ran git branch in whatever repository the contributor happened to be in, then deleted the branch again; test_broken_pipe_does_not_crash read that repository's log, and outside a repository git log only errors, so it stopped exercising the pipe.

Change

• src/core/test_support.rs (new, #[cfg(test)]): rtk_command() / pin_environment() pin LC_ALL + LANGUAGE and neutralize GIT_CONFIG_GLOBAL/GIT_CONFIG_SYSTEM; temp_git_repo() builds a throwaway repo with a local identity, so no global git config is needed at all.
• The git-status test now asserts what RTK owns — non-zero exit, message on stderr, nothing on stdout — instead of git's wording, and runs in a fresh temp dir rather than a fixed shared /tmp path.
• The three engine-spawning test helpers (search_faithful, search_compress, grep_context) and the native rg/grep spawns they compare against pin LC_ALL, so both sides speak one language. search_error_test.rs already did this for rtk; its grep side now matches.
• The two branch tests and the broken-pipe test take a temp_git_repo() and run the built binary with .current_dir().
• .claude/rules/cli-testing.md gains a "Machine independence" section: never assert on a third-party tool's wording (and watch negative assertions especially), never touch the ambient repo, plus the hostile-environment commands to check against.

Test plan

Full suite including --ignored, all green under each of:

LANG=fr_FR.UTF-8 cargo test --all -- --ignored
LC_ALL=de_DE.UTF-8 cargo test --all -- --ignored
GIT_CONFIG_GLOBAL=/dev/null GIT_CONFIG_SYSTEM=/dev/null cargo test --all -- --ignored
RIPGREP_CONFIG_PATH=<config with --smart-case -i> cargo test --all -- --ignored

Before this change the first two failed. cargo fmt --all && cargo clippy --all-targets && cargo test --all clean.

Found while reviewing #3681; unrelated to that PR's contents, so it is on its own branch off develop.

🤖 Generated with Claude Code

[aeppling]

Hey @KuSh , all good to me, thanks for contributing !