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⚠️ WARNING: documentation of unreleased features ahead

This is the current development version. You can find the documentation for v1.2.0 here. Please refer to this list for older versions.

Bats-core: Bash Automated Testing System (2018)

Latest release npm package License Continuous integration status for Linux and macOS Continuous integration status for Windows

Join the chat in bats-core/bats-core on gitter

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.

Table of contents


Supported Bash versions

The following is a list of Bash versions that are currently supported by Bats. This list is composed of platforms that Bats has been tested on and is known to work on without issues.

  • Bash versions:

    • Everything from 3.2.57(1) and higher (macOS's highest version)
  • Operating systems:

    • Arch Linux
    • Alpine Linux
    • Ubuntu Linux
    • FreeBSD 10.x and 11.x
    • macOS
    • Windows 10
  • Latest version for the following Windows platforms:

    • Git for Windows Bash (MSYS2 based)
    • Windows Subsystem for Linux
    • MSYS2
    • Cygwin


On macOS, you can install Homebrew if you haven't already, then run:

# To install with brew:
brew install bats-core


You can install the Bats npm package via:

# To install globally:
npm install -g bats

# To install into your project and save it as one of the "devDependencies" in
# your package.json:
npm install --save-dev bats

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-core
./ /usr/local

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

Installing Bats from source onto Windows Git Bash

Check out a copy of the Bats repository and install it to $HOME. This will place the bats executable in $HOME/bin, which should already be in $PATH.

git clone
cd bats-core
./ $HOME

Running Bats in Docker

There is an official image on the Docker Hub:

docker run -it bats/bats:latest --version

Building a Docker image

Check out a copy of the Bats repository, then build a container image:

git clone
cd bats-core
docker build --tag bats/bats:latest .

This creates a local Docker image called bats/bats:latest based on Alpine Linux (to push to private registries, tag it with another organisation, e.g. my-org/bats:latest).

To run Bats' internal test suite (which is in the container image at /opt/bats/test):

docker run -it bats/bats:latest /opt/bats/test

To run a test suite from a directory called test in the current directory of your local machine, mount in a volume and direct Bats to its path inside the container:

docker run -it -v "${PWD}:/code" bats/bats:latest test

/code is the working directory of the Docker image. ${PWD}/test is the location of the test directory on the local machine.

This is a minimal Docker image. If more tools are required this can be used as a base image in a Dockerfile using FROM <Docker image>. In the future there may be images based on Debian, and/or with more tools installed (curl and openssl, for example). If you require a specific configuration please search and +1 an issue or raise a new issue.

Further usage examples are in the wiki.


Bats comes with two manual pages. After installation you can view them with man 1 bats (usage manual) and man 7 bats (writing test files manual). Also, you can view the available command line options that Bats supports by calling Bats with the -h or --help options. These are the options that Bats currently supports:

Bats x.y.z
Usage: bats [OPTIONS] <tests>
       bats [-h | -v]

  <tests> is the path to a Bats test file, or the path to a directory
  containing Bats test files (ending with ".bats")

  -c, --count               Count test cases without running any tests
  -f, --filter <regex>      Only run tests that match the regular expression
  -F, --formatter <type>    Switch between formatters: pretty (default),
                              tap (default w/o term), tap13, junit
  -h, --help                Display this help message
  -j, --jobs <jobs>         Number of parallel jobs (requires GNU parallel)
  --no-tempdir-cleanup      Preserve test output temporary directory
                            Serialize test file execution instead of running
                            them in parallel (requires --jobs >1)
                            Serialize test execution within files instead of
                            running them in parallel (requires --jobs >1)
  --report-formatter <type> Switch between reporters (same options as --formatter)
  -o, --output <dir>        Directory to write report files
  -p, --pretty              Shorthand for "--formatter pretty"
  -r, --recursive           Include tests in subdirectories
  -t, --tap                 Shorthand for "--formatter tap"
  -T, --timing              Add timing information to tests
  -v, --version             Display the version number

  For more information, see

To run your tests, invoke the bats interpreter with one or more paths to test files ending with the .bats extension, or paths to directories containing test files. (bats will only execute .bats files at the top level of each directory; it will not recurse unless you specify the -r flag.)

Test cases from each file 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 --formatter tap option.

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

With --formatter junit, it is possible to output junit-compatible report files.

$ bats --formatter junit addition.bats
ok 1 addition using bc
ok 2 addition using dc

Test reports will be output in the executing directory, but may be placed elsewhere by specifying the --output flag.

$ bats --formatter junit addition.bats --output /tmp
ok 1 addition using bc
ok 2 addition using dc

Parallel Execution

By default, Bats will execute your tests serially. However, Bats supports parallel execution of tests (provided you have GNU parallel or a compatible replacement installed) using the --jobs parameter. This can result in your tests completing faster (depending on your tests and the testing hardware).

Ordering of parallised tests is not guaranteed, so this mode may break suites with dependencies between tests (or tests that write to shared locations). When enabling --jobs for the first time be sure to re-run bats multiple times to identify any inter-test dependencies or non-deterministic test behaviour.

When parallelizing, the results of a file only become visible after it has been finished. You can use --no-parallelize-across-files to get immediate output at the cost of reduced overall parallelity, as parallelization will only happen within files and files will be run sequentially.

If you have files where tests within the file would interfere with each other, you can use --no-parallelize-within-files to disable parallelization within all files. If you want more finegrained control, you can export BATS_NO_PARALLELIZE_WITHIN_FILE=true in setup_file() or outside any function to disable parallelization only within the containing file.

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.

For sample test files, see examples.

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>" ]

Note: The run helper executes its argument(s) in a subshell, so if writing tests against environmental side-effects like a variable's value being changed, these changes will not persist after run completes.

When not to use run

In some cases, using run is redundant and results in a longer and less readable code. Here are a few examples.

  1. In case you only need to check the command succeeded, it is better to not use run, since
run command args ...
echo "$output"
[ "$status" -eq 0 ]

is equivalent to

command args ...

since bats sets set -e for all tests.

  1. In case you want to hide the command output (which run does), use output redirection instead.


run command ...
[ "$status" -eq 0 ]

is equivalent to

command ... >/dev/null

Note that the output is only shown if the test case fails.

  1. In case you need to assign command output to a variable (and maybe check the command exit status), it is better to not use run, since
run command args ...
[ "$status" -eq 0 ]

is equivalent to

var=$(command args ...)

Comment syntax

External tools (like shellcheck, shfmt, and various IDE's) may not support the standard .bats syntax. Because of this, we provide a valid bash alterntative:

function invoking_foo_without_arguments_prints_usage { #@test
  run foo
  [ "$status" -eq 1 ]
  [ "${lines[0]}" = "usage: foo <filename>" ]

When using this syntax, the function name will be the title in the result output and the value checked when using --filter.

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.bash

will source the script test/test_helper.bash in your test file (limitations apply, see below). This can be useful for sharing functions to set up your environment or load fixtures. load delegates to Bash's source command after resolving relative paths.

As pointed out by @iatrou in, using the declare builtin restricts scope of a variable. Thus, since actual source-ing is performed in context of the load function, declared symbols will not be made available to callers of load.

For backwards compatibility load first searches for a file ending in .bash (e.g. load test_helper searches for test_helper.bash before it looks for test_helper). This behaviour is deprecated and subject to change, please use exact filenames instead.

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 ]

Note: setup and teardown hooks still run for skipped tests.

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.

You can also define setup_file and teardown_file, which will run once before the first test's setup and after the last test's teardown for the containing file. Variables that are exported in setup_file will be visible to all following functions (setup, the test itself, teardown, teardown_file).

Example of setup/setup_file/teardown/teardown_file call order For example the following call order would result from two files (file 1 with tests 1 and 2, and file 2 with test3) beeing tested:
setup_file # from file 1, on entering file 1
teardown_file # from file 1, on leaving file 1
setup_file # from file 2,  on enter file 2
teardown_file # from file 2,  on leaving file 2

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.

File descriptor 3 (read this if Bats hangs)

Bats makes a separation between output from the code under test and output that forms the TAP stream (which is produced by Bats internals). This is done in order to produce TAP-compliant output. In the Printing to the terminal section, there are details on how to use file descriptor 3 to print custom text properly.

A side effect of using file descriptor 3 is that, under some circumstances, it can cause Bats to block and execution to seem dead without reason. This can happen if a child process is spawned in the background from a test. In this case, the child process will inherit file descriptor 3. Bats, as the parent process, will wait for the file descriptor to be closed by the child process before continuing execution. If the child process takes a lot of time to complete (eg if the child process is a sleep 100 command or a background service that will run indefinitely), Bats will be similarly blocked for the same amount of time.

To prevent this from happening, close FD 3 explicitly when running any command that may launch long-running child processes, e.g. command_name 3>&- .

Printing to the terminal

Bats produces output compliant with version 12 of the TAP protocol. The produced TAP stream is by default piped to a pretty formatter for human consumption, but if Bats is called with the -t flag, then the TAP stream is directly printed to the console.

This has implications if you try to print custom text to the terminal. As mentioned in File descriptor 3, bats provides a special file descriptor, &3, that you should use to print your custom text. Here are some detailed guidelines to refer to:

  • Printing from within a test function:

    • To have text printed from within a test function you need to redirect the output to file descriptor 3, eg echo 'text' >&3. This output will become part of the TAP stream. You are encouraged to prepend text printed this way with a hash (eg echo '# text' >&3) in order to produce 100% TAP compliant output. Otherwise, depending on the 3rd-party tools you use to analyze the TAP stream, you can encounter unexpected behavior or errors.

    • The pretty formatter that Bats uses by default to process the TAP stream will filter out and not print text output to file descriptor 3.

    • Text that is output directly to stdout or stderr (file descriptor 1 or 2), ie echo 'text' is considered part of the test function output and is printed only on test failures for diagnostic purposes, regardless of the formatter used (TAP or pretty).

  • Printing from within the setup or teardown functions: The same hold true as for printing with test functions.

  • Printing outside test or setup/teardown functions:

    • Regardless of where text is redirected to (stdout, stderr or file descriptor 3) text is immediately visible in the terminal.

    • Text printed in such a way, will disable pretty formatting. Also, it will make output non-compliant with the TAP spec. The reason for this is that each test file is evaluated n+1 times (as mentioned earlier). The first run will cause such output to be produced before the plan line is printed, contrary to the spec that requires the plan line to be either the first or the last line of the output.

    • Due to internal pipes/redirects, output to stderr is always printed first.

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_SUITE_TEST_NUMBER is the (1-based) index of the current test case in the test suite (over all files).
  • $BATS_TMPDIR is the location to a directory that may be used to store temporary files.
  • $BATS_FILE_EXTENSION (default: bats) specifies the extension of test files that should be found when running a suite (via bats [-r] suite_folder/)

Libraries and Add-ons

Bats supports loading external assertion libraries and helpers. Those under bats-core are officially supported libraries (integration tests welcome!):

and some external libraries, supported on a "best-effort" basis:


bin/bats --tap test

See also the CI settings for the current test environment and scripts.


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.


For now see the docs folder for project guides, work with us on the wiki or look at the other communication channels.


  • We are #bats on freenode;
  • Or leave a message on gitter.

Version history

See docs/


What's the plan and why?

Tuesday, September 19, 2017: This was forked from Bats at commit 0360811. It was created via git clone --bare and git push --mirror.

This bats-core repo is the community-maintained Bats project.

Why was this fork created?

There was an initial call for maintainers for the original Bats repository, but write access to it could not be obtained. With development activity stalled, this fork allowed ongoing maintenance and forward progress for Bats.


© 2017-2020 bats-core organization

© 2011-2016 Sam Stephenson

Bats is released under an MIT-style license; see for details.

See the parent project at GitHub or the AUTHORS file for the current project maintainer team.

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