Brat (Brutal Runner for Automated Tests) is a parallel TAP testing harness for the POSIX shell, written entirely in shell and awk with no external dependencies. Inspired by Bats (Bash Automated Testing System), it works with any POSIX-compliant shell and has built-in parallel execution via a FIFO, unlike Bats which requires GNU parallel and Bash. Tests are written using a special `@test` syntax preprocessed into shell functions running under `set -eu`, so every command acts as an assertion. Output is captured to files (`$stdout`, `$stderr`) rather than in-memory strings. The tool is intentionally small (~1000 lines), embeddable directly into projects, and tested across Alpine, Debian, Fedora, FreeBSD, and macOS. It exposes composable subcommands (`plan-build`, `plan-run`, `test-run`) for pipeline integration and outputs TAP version 14 with optional color formatting.
