bats-mock

Mocking/stubbing library for BATS (Bash Automated Testing System)

Installation

git

The recommended installation is via git submodule. Assuming your project's bats tests are in test:

git submodule add https://github.com/jasonkarns/bats-mock test/helpers/mocks
git commit -am 'added bats-mock module'

then in test/test_helper.bash:

load helpers/mocks/stub

[!note] Consider using git's sparse-checkout if you're concerned with the non-essential files cluttering your repository.

npm

Also available as an npm module if you're into that sort of thing.

npm install --save-dev bats-mock

then in test/test_helper.bash:

load ../node_modules/bats-mock/stub

Usage

After loading bats-mock/stub you have two new functions defined:

• stub: for creating new stubs, along with a plan with expected args and the results to return when called.
• unstub: for cleaning up, and also verifying that the plan was fullfilled.

Stubbing

The stub function takes a program name as its first argument; any remaining arguments go into the stub plan.

Each plan line represents an expected invocation: a list of expected arguments followed by the command to execute, separated with a colon.

arg1 arg2 ... : only_run if args matched

The expected args (and the colon) is optional.

So, in order to stub date, we could use something like this in a test case (where format_date is the function under test, relying on data from the date command):

load helper

# this is the "code under test"
# it would normally be in another file
format_date() {
  date -r 222
}

setup() {
  _DATE_ARGS='-r 222'
  stub date \
      "${_DATE_ARGS} : echo 'I am stubbed!'" \
      "${_DATE_ARGS} : echo 'Wed Dec 31 18:03:42 CST 1969'"
}

teardown() {
  unstub date
}

@test "date format util formats date with expected arguments" {
  result="$(format_date)"
  [ "$result" == 'I am stubbed!' ]

  result="$(format_date)"
  [ "$result" == 'Wed Dec 31 18:03:42 CST 1969' ]
}

This verifies that format_date indeed called date using the args defined in ${_DATE_ARGS} (which can not be declared in the test-case with local), and made proper use of the output of it.

The plan is verified, one by one, as the calls come in. Finally, when the stub is removed with unstub, there is a final check to ensure there are no remaining un-met plans (which would indicated an expected invocation that did not occur).

Unstubbing

Once the test case is done, you should call unstub <program> in order to clean up the temporary files, and make a final check that all the plans have been met for the stub.

How it works

Under the covers, bats-mock uses three scripts to manage the stubbed programs/functions.

First, it is the command (or program) itself, which when the stub is created is placed in (or rather, the binstub script is sym-linked to) ${BATS_MOCK_BINDIR}/${program} (which is added to your PATH when loading the stub library). Secondly, it creates a stub plan, based on the arguments passed when creating the stub. And finally, during execution, the command invocations are tracked in a stub run file which is checked once the command is unstub'ed. The ${program}-stub-[plan|run] files are both in ${BATS_MOCK_TMPDIR}.

Caveat

If you stub functions, make sure to unset them, or the stub script wan't be called, as the function will shadow the binstub script on the PATH.

Credits

Extracted from the ruby-build test suite. Many thanks to its author and contributors: Sam Stephenson and Mislav Marohnić.