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 are any failures, 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.

Writing Bats tests

The run helper

If you're using Bats, you're probably most interested in testing a command's exit status and output. Bats includes a run helper that invokes its arguments as a command, saves the exit status and output into special global variables, and then returns with a 0 status code so you can continue to make assertions in your test case.

For example, let's say you're testing that the foo command, when passed a nonexistent filename, exits with a 1 status code and prints an error message.

@test "invoking foo with a nonexistent file prints an error" {
  run foo nonexistent_filename
  [ "$status" -eq 1 ]
  [ "$output" = "foo: no such file 'nonexistent_filename'" ]
}

The $status variable contains the status code of the command, and the $output variable contains the combined contents of the command's standard output and standard error streams.

A third special variable, the $lines array, is available for easily accessing individual lines of output. For example, if you want to test that invoking foo without any arguments prints usage information on the first line:

@test "invoking foo without arguments prints usage" {
  run foo
  [ "$status" -eq 1 ]
  [ "${lines[0]}" = "usage: foo <filename>" ]
}

The load command

You may want to share common code across multiple test files. Bats includes a convenient load command for sourcing a Bash source file relative to the location of the current test file. For example, if you have a Bats test in test/foo.bats, the command

load test_helper

will source the script test/test_helper.bash in your test file. This can be useful for sharing functions to set up your environment or load fixtures.

Special variables

There are several global variables you can use to introspect on Bats tests:

• $BATS_TEST_FILENAME is the fully expanded path to the Bats test file.
• $BATS_TEST_DIRNAME is the directory in which the Bats test file is located.
• $BATS_TEST_NAMES is an array of function names for each test case.
• $BATS_TEST_NAME is the name of the function containing the current test case.
• $BATS_TEST_DESCRIPTION is the description of the current test case.
• $BATS_TEST_NUMBER is the (1-based) index of the current test case in the test file.
• $BATS_TMPDIR is the location to a directory that may be used to store temporary files.

Installing Bats

Check out a copy of the Bats repository. Then, either add the Bats bin directory to your $PATH, or run the provided install.sh command with the location to the prefix in which you want to install Bats. For example, to install Bats into /usr/local,

$ git clone https://github.com/sstephenson/bats.git
$ cd bats
$ ./install.sh /usr/local

Note that you may need to run install.sh with sudo if you do not have permission to write to the installation prefix.

Development

The Bats source code repository is hosted on GitHub. There you can file bugs on the issue tracker or submit tested pull requests for review.

See the Bats test suite for examples.

Version history

0.1.0 (December 30, 2011)

• Initial public release.

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© 2011 Sam Stephenson. Bats is released under an MIT-style license; see LICENSE for details.