0.4.0 • Public • Published

Bats: 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 ]

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

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.

Running tests

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. 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.

When you run Bats from a terminal, you'll see output as each test is performed, with a check-mark next to the test's name if it passes or an "X" if it fails.

$ bats addition.bats
 ✓ addition using bc
 ✓ addition using dc

2 tests, 0 failures

If Bats is not connected to a terminal—in other words, if you run it from a continuous integration system, or redirect its output to a file—the results are displayed in human-readable, machine-parsable TAP format.

You can force TAP output from a terminal by invoking Bats with the --tap option.

$ bats --tap addition.bats
ok 1 addition using bc
ok 2 addition using dc

Test suites

You can invoke the bats interpreter with multiple test file arguments, or with a path to a directory containing multiple .bats files. Bats will run each test file individually and aggregate the results. If any test case fails, bats exits with a 1 status code.

Writing tests

Each Bats test file is evaluated n+1 times, where n is the number of test cases in the file. The first run counts the number of test cases, then iterates over the test cases and executes each one in its own process.

For more details about how Bats evaluates test files, see Bats Evaluation Process on the wiki.

run: Test other commands

Many Bats tests need to run a command and then make assertions about its 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>" ]

load: Share common code

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.

skip: Easily skip tests

Tests can be skipped by using the skip command at the point in a test you wish to skip.

@test "A test I don't want to execute for now" {
  run foo
  [ "$status" -eq 0 ]

Optionally, you may include a reason for skipping:

@test "A test I don't want to execute for now" {
  skip "This command will return zero soon, but not now"
  run foo
  [ "$status" -eq 0 ]

Or you can skip conditionally:

@test "A test which should run" {
  if [ foo != bar ]; then
    skip "foo isn't bar"
  run foo
  [ "$status" -eq 0 ]

setup and teardown: Pre- and post-test hooks

You can 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.

Code outside of test cases

You can include code in your test file outside of @test functions. For example, this may be useful if you want to check for dependencies and fail immediately if they're not present. However, any output that you print in code outside of @test, setup or teardown functions must be redirected to stderr (>&2). Otherwise, the output may cause Bats to fail by polluting the TAP stream on stdout.

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 from source

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

$ git clone
$ cd bats
$ ./ /usr/local

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


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.

For real-world examples from open-source projects using Bats, see Projects Using Bats on the wiki.

To learn how to set up your editor for Bats syntax highlighting, see Syntax Highlighting on the wiki.

Version history

0.4.0 (August 13, 2014)

  • Improved the display of failing test cases. Bats now shows the source code of failing test lines, along with full stack traces including function names, filenames, and line numbers.
  • Improved the display of the pretty-printed test summary line to include the number of skipped tests, if any.
  • Improved the speed of the preprocessor, dramatically shortening test and suite startup times.
  • Added support for absolute pathnames to the load helper.
  • Added support for single-line @test definitions.
  • Added bats(1) and bats(7) manual pages.
  • Modified the bats command to default to TAP output when the $CI variable is set, to better support environments such as Travis CI.

0.3.1 (October 28, 2013)

  • Fixed an incompatibility with the pretty formatter in certain environments such as tmux.
  • Fixed a bug where the pretty formatter would crash if the first line of a test file's output was invalid TAP.

0.3.0 (October 21, 2013)

  • Improved formatting for tests run from a terminal. Failing tests are now colored in red, and the total number of failing tests is displayed at the end of the test run. When Bats is not connected to a terminal (e.g. in CI runs), or when invoked with the --tap flag, output is displayed in standard TAP format.
  • Added the ability to skip tests using the skip command.
  • Added a message to failing test case output indicating the file and line number of the statement that caused the test to fail.
  • Added "ad-hoc" test suite support. You can now invoke bats with multiple filename or directory arguments to run all the specified tests in aggregate.
  • Added support for test files with Windows line endings.
  • Fixed regular expression warnings from certain versions of Bash.
  • Fixed a bug running tests containing lines that begin with -e.

0.2.0 (November 16, 2012)

  • Added test suite support. The bats command accepts a directory name containing multiple test files to be run in aggregate.
  • Added the ability to count the number of test cases in a file or suite by passing the -c flag to bats.
  • Preprocessed sources are cached between test case runs in the same file for better performance.

0.1.0 (December 30, 2011)

  • Initial public release.

© 2014 Sam Stephenson. Bats is released under an MIT-style license; see LICENSE for details.




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