Bats: the Bash Automated Testing System

Bats is a TAP-compliant testing framework for Bash. It provides a simple way to verify that the UNIX programs you write behave as expected.

A Bats test file is a Bash script with special syntax for defining test cases. Under the hood, each test case is just a function with a description.

#!/usr/bin/env bats

@test "addition using bc" {
  result="$(echo 2+2 | bc)"
  [ "$result" -eq 4 ]
}

@test "addition using dc" {
  result="$(echo 2 2+p | dc)"
  [ "$result" -eq 4 ]
}

Test cases consist of standard shell commands. Bats makes use of Bash's errexit (set -e) option when running test cases. If every command in the test case exits with a 0 status code (success), the test passes. In this way, each line is an assertion of truth.

To run your tests, invoke the bats interpreter with a path to a test file. The file's test cases are run sequentially and in isolation, and the results are written to standard output in human-readable TAP format. If all the test cases pass, bats exits with a 0 status code. If there is a failure, bats exits with a 1 status code.

$ bats addition.bats
1..2
ok 1 addition using bc
ok 2 addition using dc
$ echo $?
0

You can also define special setup and teardown functions which run before and after each test case, respectively. Use these to load fixtures, set up your environment, and clean up when you're done.

Bats is most useful when testing software written in Bash, but you can use it to test any UNIX program.