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bats - Man Page

Bats test file format


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 ]

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.

Tagging tests

Each test has a list of tags attached to it. Without specification, this list is empty. Tags can be defined in two ways. The first being # bats test_tags=:

# bats test_tags=tag:1, tag:2, tag:3 @test "second test" { # ... }

@test "second test" { # ... }

These tags (tag:1, tag:2, tag:3) will be attached to the test first test. The second test will have no tags attached. Values defined in the # bats test_tags= directive will be assigned to the next @test that is being encountered in the file and forgotten after that. Only the value of the last # bats test_tags= directive before a given test will be used.

Sometimes, we want to give all tests in a file a set of the same tags. This can be achieved via # bats file_tags=. They will be added to all tests in the file after that directive. An additional # bats file_tags= directive will override the previously defined values:

@test "Zeroth test" {
  # will have no tags

# bats file_tags=a:b
# bats test_tags=c:d

@test "First test" {
  # will be tagged a:b, c:d

# bats file_tags=

@test "Second test" {
  # will have no tags

Tags are case sensitive and must only consist of alphanumeric characters and _, -, or :. They must not contain whitespaces! The colon is intended as a separator for (recursive) namespacing.

Tag lists must be separated by commas and are allowed to contain whitespace. They must not contain empty tags like test_tags=,b (first tag is empty), test_tags=a,,c, test_tags=a, ,c (second tag is only whitespace/empty), test_tags=a,b, (third tag is empty).

Every tag starting with bats: (case insensitive!) is reserved for Bats´ internal use:


If any test with the tag bats:focus is encountered in a test suite, only those tagged with this tag will be executed. To prevent the CI from silently running on a subset of tests due to an accidentally committed bats:focus tag, the exit code of successful runs will be overridden to 1.

Should you require the true exit code, e.g. for a git bisect operation, you can disable this behavior by setting BATS_NO_FAIL_FOCUS_RUN=1 when running bats, but make sure to not commit this to CI!

The Run Helper

Usage: run [OPTIONS] [--]

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 (optionally) checks exit status against a given expected value. If successful, run 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 -1 foo nonexistent_filename
  [ "$output" = "foo: no such file ´nonexistent_filename´" ]

The -1 as first argument tells run to expect 1 as an exit status, and to fail if the command exits with any other value. On failure, both actual and expected values will be displayed, along with the invoked command and its output:

(in test file test.bats, line 2)
 `run -1 foo nonexistent_filename´ failed, expected exit code 1, got 127

This error indicates a possible problem with the installation or configuration of foo; note that a simple [ $status != 0 ] test would not have caught this kind of failure.

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 -1 foo
  [ "${lines[0]}" = "usage: foo <filename>" ]

By default run leaves out empty lines in ${lines[@]}. Use run --keep-empty-lines to retain them.

Additionally, you can use --separate-stderr to split stdout and stderr into $output/$stderr and ${lines[@]}/${stderr_lines[@]}.

All additional parameters to run should come before the command. If you want to run a command that starts with -, prefix it with -- to prevent run from parsing it as an option.

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.

The Bats_load_library Command

Some libraries are installed on the system, e.g. by npm or brew. These should not be loaded, as their path depends on the installation method. Instead, one should use bats_load_library together with setting BATS_LIB_PATH, a PATH-like colon-delimited variable.

bats_load_library has two modes of resolving requests:

  1. by relative path from the BATS_LIB_PATH to a file in the library
  2. by library name, expecting libraries to have a load.bash entrypoint

For example if your BATS_LIB_PATH is set to ~/.bats/libs:/usr/lib/bats, then bats_load_library test_helper would look for existing files with the following paths:

The first existing file in this list will be sourced.

If you want to load only part of a library or the entry point is not named load.bash, you have to include it in the argument: bats_load_library library_name/file_to_load will try

Apart from the changed lookup rules, bats_load_library behaves like load.

Note: As seen above load.bash is the entry point for libraries and meant to load more files from its directory or other libraries.

Note: Obviously, the actual BATS_LIB_PATH is highly dependent on the environment. To maintain a uniform location across systems, (distribution) package maintainers are encouraged to use /usr/lib/bats/ as the install path for libraries where possible. However, if the package manager has another preferred location, like npm or brew, you should use this instead.

The Skip Command

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 -0 foo

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 -0 foo

Or you can skip conditionally:

@test "A test which should run" {
  if [ foo != bar ]; then
    skip "foo isn´t bar"

  run -0 foo

The Bats_require_minimum_version Command

Code for newer versions of Bats can be incompatible with older versions. In the best case this will lead to an error message and a failed test suite. In the worst case, the tests will pass erroneously, potentially masking a failure.

Use bats_require_minimum_version <Bats version number> to avoid this. It communicates in a concise manner, that you intend the following code to be run under the given Bats version or higher.

Additionally, this function will communicate the current Bats version floor to subsequent code, allowing e.g. Bats´ internal warning to give more informed warnings.

Note: By default, calling bats_require_minimum_version with versions before Bats 1.7.0 will fail regardless of the required version as the function is not available. However, you can use the bats-backports plugin (https://github.com/bats-core/bats-backports) to make your code usable with older versions, e.g. during migration while your CI system is not yet upgraded.

Setup and Teardown Functions

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:

See Also

bash(1), bats(1)

Referenced By


November 2022 bats-core Bash Automated Testing System