How to Safely Test Bash Scripts with the Bach Framework

This article presents Bach, a tiny (~50 kB) Bash unit‑testing framework designed to prevent accidental execution of dangerous commands such as rm -rf during script development.

Bach Overview

By sourcing the bach.sh script, developers gain a collection of @ -prefixed APIs that mock or safely invoke commands, ensuring that no real system binaries are run unless explicitly specified with an absolute path.

Getting Started

Download the framework and source it in your test file: source /path/to/bach.sh After sourcing, the framework provides a set of testing helpers.

Key API – @do-not-panic

The @do-not-panic API can be placed inside a test method that contains dangerous commands; it prevents accidental execution by mocking the command.

Writing Tests

Test methods must start with test- and corresponding assertion methods end with -assert. The framework matches them automatically.

test-delete-files() {
    rm -rf /tmp/some_dir
}

test-delete-files-assert() {
    # assertions here
}

If the command and its arguments differ from the expected ones, the test fails.

Mocking and Direct Execution

APIs beginning with @ can either mock commands (e.g., @mock-command) or invoke them directly when needed. Special handling is provided for command and xargs.

How Bach Works

Bach validates the invocation of commands, checking that the expected parameters or options are passed, rather than evaluating command output. No command found in $PATH is executed unless a full path is specified.

Compared with other Bash test tools such as Bats or Shunit2, which actually run system binaries, Bach offers a safe environment for testing destructive commands.

Limitations

It cannot block commands invoked with an absolute path.

I/O redirection cannot be prevented.

Adoption

Companies such as BMW Group and Huawei are already using Bach, and the project continues to receive updates.

Resources

GitHub repository: https://github.com/bach-sh/bach/blob/master/README-cn.md Test examples:

https://github.com/bach-sh/bach/blob/master/tests/bach-testing-framework.test.sh