DESCRIPTION

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.

THE RUN HELPER

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>" ]
}

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 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" {
  skip
  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"
  fi
  run foo
  [ "$status" -eq 0 ]
}

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:

•

$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.