ifdef::backend-manpage[]
= BASH_UNIT(1)

== NAME
endif::[]

ifndef::backend-manpage[]
image::img/bu_50.png[bash_unit]
endif::[]

bash_unit - bash unit testing enterprise edition framework for professionals!

== Synopsis

*bash_unit* [-f tap] [-p <pattern>] [-s <pattern>] [-r] [test_file]

== Description

*bash_unit* allows you to write unit tests (functions starting with *test*),
run them and, in case of failure, displays the stack trace
with source file and line number indications to locate the problem.

You might want to take a look at link:getting_started[how to get started]
before continuing reading this documentation.

The following functions are available in your tests (see below for detailed documentation):

* `fail [message]`
* `assert <assertion> [message]`
* `assert_fail <assertion> [message]`
* `assert_status_code <expected_status_code> <assertion> [message]`
* `assert_equals <expected> <actual> [message]`
* `assert_not_equals <unexpected> <actual> [message]`
* `assert_matches <expected-regex> <actual> [message]`
* `assert_not_matches <unexpected-regex> <actual> [message]`
* `assert_within_delta <expected num> <actual num> <max delta> [message]`
* `assert_no_diff <expected> <actual> [message]`
* `skip_if <condition> <pattern>`
* `fake <command> [replacement code]`

ifndef::backend-manpage[]
image::img/demo.gif[demo]
endif::[]

_(by the way, the documentation you are reading is itself tested with bash-unit)_

*bash_unit* is free software you may contribute to. See link:CONTRIBUTING.md[CONTRIBUTING.md].


== Options

*-p* _pattern_::
  filters tests to run based on the given pattern.
  You can specify several patterns by repeating this option
  for each pattern.

*-s* _pattern_::
  skip tests which name matches the given pattern.
  You can specify several patterns by repeating this option
  for each pattern.
  Tests will appear in *bash_unit* output as _skipped_.
  (see also _skip_if_)

*-r*::
  executes test cases in random order.
  Only affects the order within a test file (files are always
  executed in the order in which they are specified on the
  command line).

*-f* _output_format_::
  specify an alternative output format.
  The only supported value is *tap*.

*-q*::
  quiet mode.
  Will only output the status of each test with no further
  information even in case of failure.

ifndef::backend-manpage[]

== How to install *bash_unit*

=== installing on Archlinux

*bash_unit* package is available on Archlinux through AUR. In order to install, issue the following command :

    yaourt -Sys bash_unit

=== installing via link:https://nixos.org/[Nix/NixOS]

*bash_unit* package has been added to link:https://github.com/nixos/nixpkgs[nixpkgs]. You can use it with the following command:

    nix-shell -p bash_unit

=== installing via link:https://brew.sh[Homebrew]

*bash_unit* is available by invoking brew:

    brew install bash_unit

=== other installation

This will install *bash_unit* in your current working directory:

    curl -s https://raw.githubusercontent.com/pgrange/bash_unit/master/install.sh | bash

You can also download it from the https://github.com/pgrange/bash_unit/releases[release page].

endif::[]

=== GitHub Actions

Here is an example of how you could integrate *bash_unit* with https://docs.github.com/fr/actions[GitHub Actions]:

```
name: bash_unit tests
on:
  push:
    branches: [ main ]
  pull_request:
    branches: [ main ]

jobs:
  ubuntu:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v4
    - name: Unit testing with bash_unit
      run: |
        curl -s https://raw.githubusercontent.com/pgrange/bash_unit/master/install.sh | bash
        FORCE_COLOR=true ./bash_unit tests/test_*
```

See this bash_unit https://github.com/pgrange/bash_unit_getting_started[getting started gitlab project] for a working example.

=== GitLab CI

Here is an example of how you could integrate *bash_unit* with https://docs.gitlab.com/ee/ci/[GitLab CI]:

```
test:
  image: debian
  script:
    - apt-get update
    - apt-get install --no-install-recommends -y curl ca-certificates
    - curl -s https://raw.githubusercontent.com/pgrange/bash_unit/master/install.sh | bash
    - FORCE_COLOR=true ./bash_unit tests/test_*
```

See this bash_unit https://gitlab.com/pgrange/bash_unit_getting_started[getting started gitlab project] for a working example.

=== pre-commit hook

You can run `+bash_unit+` as a https://pre-commit.com[pre-commit] hook.

Add the following to your pre-commit configuration. By default it will run scripts that are identified as shell scripts that match the path `+^tests/(.*/)?test_.*\.sh$+`.

[.pre-commit-config,yaml]
```
repos:
  - repo: https://github.com/pgrange/bash_unit
    rev: v2.2.0
    hooks:
      - id: bash-unit
        always-run: true
```

== How to run tests

To run tests, simply call *bash_unit* with all your tests files as parameter. For instance to run some *bash_unit* tests, from *bash_unit* directory:

```test
./bash_unit tests/test_core.sh
```

```output
Running tests in tests/test_core.sh
	Running test_assert_equals_fails_when_not_equal ... SUCCESS
	Running test_assert_equals_succeed_when_equal ... SUCCESS
	Running test_assert_fails ... SUCCESS
	Running test_assert_fails_fails ... SUCCESS
	Running test_assert_fails_succeeds ... SUCCESS
	Running test_assert_matches_fails_when_not_matching ... SUCCESS
	Running test_assert_matches_succeed_when_matching ... SUCCESS
	Running test_assert_no_diff_fails_when_diff ... SUCCESS
	Running test_assert_no_diff_succeeds_when_no_diff ... SUCCESS
	Running test_assert_not_equals_fails_when_equal ... SUCCESS
	Running test_assert_not_equals_succeeds_when_not_equal ... SUCCESS
	Running test_assert_not_matches_fails_when_matching ... SUCCESS
	Running test_assert_not_matches_succeed_when_not_matching ... SUCCESS
	Running test_assert_shows_stderr_on_failure ... SUCCESS
	Running test_assert_shows_stdout_on_failure ... SUCCESS
	Running test_assert_status_code_fails ... SUCCESS
	Running test_assert_status_code_succeeds ... SUCCESS
	Running test_assert_succeeds ... SUCCESS
	Running test_assert_within_delta_fails ... SUCCESS
	Running test_assert_within_delta_succeeds ... SUCCESS
	Running test_fail_fails ... SUCCESS
	Running test_fail_prints_failure_message ... SUCCESS
	Running test_fail_prints_where_is_error ... SUCCESS
	Running test_fake_actually_fakes_the_command ... SUCCESS
	Running test_fake_can_fake_inline ... SUCCESS
	Running test_fake_echo_stdin_when_no_params ... SUCCESS
	Running test_fake_exports_faked_in_subshells ... SUCCESS
	Running test_fake_transmits_params_to_fake_code ... SUCCESS
	Running test_fake_transmits_params_to_fake_code_as_array ... SUCCESS
	Running test_should_pretty_format_even_when_LANG_is_unset ... SUCCESS
Overall result: SUCCESS
```

You might also want to run only specific tests, you may do so with the
_-p_ option. This option accepts a pattern as parameter and filters test
functions against this pattern.

```test
./bash_unit -p fail_fails -p assert tests/test_core.sh
```

```output
Running tests in tests/test_core.sh
	Running test_assert_equals_fails_when_not_equal ... SUCCESS
	Running test_assert_equals_succeed_when_equal ... SUCCESS
	Running test_assert_fails ... SUCCESS
	Running test_assert_fails_fails ... SUCCESS
	Running test_assert_fails_succeeds ... SUCCESS
	Running test_assert_matches_fails_when_not_matching ... SUCCESS
	Running test_assert_matches_succeed_when_matching ... SUCCESS
	Running test_assert_no_diff_fails_when_diff ... SUCCESS
	Running test_assert_no_diff_succeeds_when_no_diff ... SUCCESS
	Running test_assert_not_equals_fails_when_equal ... SUCCESS
	Running test_assert_not_equals_succeeds_when_not_equal ... SUCCESS
	Running test_assert_not_matches_fails_when_matching ... SUCCESS
	Running test_assert_not_matches_succeed_when_not_matching ... SUCCESS
	Running test_assert_shows_stderr_on_failure ... SUCCESS
	Running test_assert_shows_stdout_on_failure ... SUCCESS
	Running test_assert_status_code_fails ... SUCCESS
	Running test_assert_status_code_succeeds ... SUCCESS
	Running test_assert_succeeds ... SUCCESS
	Running test_assert_within_delta_fails ... SUCCESS
	Running test_assert_within_delta_succeeds ... SUCCESS
	Running test_fail_fails ... SUCCESS
Overall result: SUCCESS
```

You can combine the _-p_ option with _-s_ to skip some of the tests. This option accepts a pattern
as parameter and mark as skipped any test function which matches this pattern.

```test
./bash_unit -p fail_fails -p assert -s no -s status tests/test_core.sh
```

```output
Running tests in tests/test_core.sh
	Running test_assert_equals_fails_when_not_equal ... SKIPPED
	Running test_assert_matches_fails_when_not_matching ... SKIPPED
	Running test_assert_no_diff_fails_when_diff ... SKIPPED
	Running test_assert_no_diff_succeeds_when_no_diff ... SKIPPED
	Running test_assert_not_equals_fails_when_equal ... SKIPPED
	Running test_assert_not_equals_succeeds_when_not_equal ... SKIPPED
	Running test_assert_not_matches_fails_when_matching ... SKIPPED
	Running test_assert_not_matches_succeed_when_not_matching ... SKIPPED
	Running test_assert_status_code_fails ... SKIPPED
	Running test_assert_status_code_succeeds ... SKIPPED
	Running test_assert_equals_succeed_when_equal ... SUCCESS
	Running test_assert_fails ... SUCCESS
	Running test_assert_fails_fails ... SUCCESS
	Running test_assert_fails_succeeds ... SUCCESS
	Running test_assert_matches_succeed_when_matching ... SUCCESS
	Running test_assert_shows_stderr_on_failure ... SUCCESS
	Running test_assert_shows_stdout_on_failure ... SUCCESS
	Running test_assert_succeeds ... SUCCESS
	Running test_assert_within_delta_fails ... SUCCESS
	Running test_assert_within_delta_succeeds ... SUCCESS
	Running test_fail_fails ... SUCCESS
Overall result: SUCCESS
```

*bash_unit* supports the http://testanything.org/[Test Anything Protocol] so you can ask for a tap formatted
output with the _-f_ option.

```test
./bash_unit -f tap tests/test_core.sh
```

```output
# Running tests in tests/test_core.sh
ok - test_assert_equals_fails_when_not_equal
ok - test_assert_equals_succeed_when_equal
ok - test_assert_fails
ok - test_assert_fails_fails
ok - test_assert_fails_succeeds
ok - test_assert_matches_fails_when_not_matching
ok - test_assert_matches_succeed_when_matching
ok - test_assert_no_diff_fails_when_diff
ok - test_assert_no_diff_succeeds_when_no_diff
ok - test_assert_not_equals_fails_when_equal
ok - test_assert_not_equals_succeeds_when_not_equal
ok - test_assert_not_matches_fails_when_matching
ok - test_assert_not_matches_succeed_when_not_matching
ok - test_assert_shows_stderr_on_failure
ok - test_assert_shows_stdout_on_failure
ok - test_assert_status_code_fails
ok - test_assert_status_code_succeeds
ok - test_assert_succeeds
ok - test_assert_within_delta_fails
ok - test_assert_within_delta_succeeds
ok - test_fail_fails
ok - test_fail_prints_failure_message
ok - test_fail_prints_where_is_error
ok - test_fake_actually_fakes_the_command
ok - test_fake_can_fake_inline
ok - test_fake_echo_stdin_when_no_params
ok - test_fake_exports_faked_in_subshells
ok - test_fake_transmits_params_to_fake_code
ok - test_fake_transmits_params_to_fake_code_as_array
ok - test_should_pretty_format_even_when_LANG_is_unset
1..30
```

== How to write tests

Write your test functions in a file. The name of a test function has to start with *test*. Only functions starting with *test* will be tested.

Use the *bash_unit* assertion functions in your test functions, see below.

You may write a *setup* function that will be executed before each test is run.

You may write a *teardown* function that will be executed after each test is run.

You may write a *setup_suite* function that will be executed only once before all the tests of your test file.

You may write a *teardown_suite* function that will be executed only once after all the tests of your test file.

If you write code outside of any bash function, this code will be executed once at test file loading time since
your file is a bash script and *bash_unit* sources it before running your tests. It is suggested to write a
*setup_suite* function and avoid any code outside a bash function. you must not use any bash_unit assertion
in setup_suite or use exit in setup_suite for teardown_suite to be run.
See https://github.com/pgrange/bash_unit/issues/43[issue 43] for more details.

If you want to keep an eye on a test not yet implemented, prefix the name of the function by *todo* instead of test.
Test to do are not executed and do not impact the global status of your test suite but are displayed in *bash_unit* output.

*bash_unit* changes the current working directory to the one of the running test file. If you need to access files from your test code, for instance the script under test, use path relative to the test file.

You may need to change the behavior of some commands to create conditions for your code under test to behave as expected. The *fake* function may help you to do that, see below.

== Test functions

*bash_unit* supports several shell oriented assertion functions.

=== *fail*

    fail [message]

Fails the test and displays an optional message.

```test
test_can_fail() {
  fail "this test failed on purpose"
}
```

```output
	Running test_can_fail ... FAILURE
this test failed on purpose
doc:2:test_can_fail()
```

=== *assert*

    assert <assertion> [message]

Evaluates _assertion_ and fails if _assertion_ fails.

_assertion_ fails if its evaluation returns a status code different from 0.

In case of failure, the standard output and error of the evaluated _assertion_ is displayed. The optional message is also displayed.

```test
test_assert_fails() {
  assert false "this test failed, obviously"
}
test_assert_succeed() {
  assert true
}
```

```output
	Running test_assert_fails ... FAILURE
this test failed, obviously
doc:2:test_assert_fails()
	Running test_assert_succeed ... SUCCESS
```

But you probably want to assert less obvious facts.

```test
code() {
  touch /tmp/the_file
}

test_code_creates_the_file() {
  code

  assert "test -e /tmp/the_file"
}

test_code_makes_the_file_executable() {
  code

  assert "test -x /tmp/the_file" "/tmp/the_file should be executable"
}
```

```output
	Running test_code_creates_the_file ... SUCCESS
	Running test_code_makes_the_file_executable ... FAILURE
/tmp/the_file should be executable
doc:14:test_code_makes_the_file_executable()
```

It may also be fun to use assert to check for the expected content of a file.

```test
code() {
  echo 'not so cool' > /tmp/the_file
}

test_code_write_appropriate_content_in_the_file() {
  code

  assert "diff <(echo 'this is cool') /tmp/the_file"
}
```

```output
	Running test_code_write_appropriate_content_in_the_file ... FAILURE
out> 1c1
out> < this is cool
out> ---
out> > not so cool
doc:8:test_code_write_appropriate_content_in_the_file()
```

=== *assert_fail*

    assert_fail <assertion> [message]

Asserts that _assertion_ fails. This is the opposite of *assert*.

_assertion_ fails if its evaluation returns a status code different from 0.

If the evaluated expression does not fail, then *assert_fail* will fail and display the standard output and error of the evaluated _assertion_. The optional message is also displayed.

```test
code() {
  echo 'not so cool' > /tmp/the_file
}

test_code_does_not_write_cool_in_the_file() {
  code

  assert_fails "grep cool /tmp/the_file" "should not write 'cool' in /tmp/the_file"
}

test_code_does_not_write_this_in_the_file() {
  code

  assert_fails "grep this /tmp/the_file" "should not write 'this' in /tmp/the_file"
}
```

```output
	Running test_code_does_not_write_cool_in_the_file ... FAILURE
should not write 'cool' in /tmp/the_file
out> not so cool
doc:8:test_code_does_not_write_cool_in_the_file()
	Running test_code_does_not_write_this_in_the_file ... SUCCESS
```

=== *assert_status_code*

    assert_status_code <expected_status_code> <assertion> [message]

Checks for a precise status code of the evaluation of _assertion_.

It may be useful if you want to distinguish between several error conditions in your code.

In case of failure, the standard output and error of the evaluated _assertion_ is displayed. The optional message is also displayed.

```test
code() {
  exit 23
}

test_code_should_fail_with_code_25() {
  assert_status_code 25 code
}
```

```output
	Running test_code_should_fail_with_code_25 ... FAILURE
 expected status code 25 but was 23
doc:6:test_code_should_fail_with_code_25()
```

=== *assert_equals*

    assert_equals <expected> <actual> [message]

Asserts for equality of the two strings _expected_ and _actual_.

```test
test_obvious_inequality_with_assert_equals(){
  assert_equals "a string" "another string" "a string should be another string"
}
test_obvious_equality_with_assert_equals(){
  assert_equals a a
}

```

```output
	Running test_obvious_equality_with_assert_equals ... SUCCESS
	Running test_obvious_inequality_with_assert_equals ... FAILURE
a string should be another string
 expected [a string] but was [another string]
doc:2:test_obvious_inequality_with_assert_equals()
```

=== *assert_not_equals*

    assert_not_equals <unexpected> <actual> [message]

Asserts for inequality of the two strings _unexpected_ and _actual_.

```test
test_obvious_equality_with_assert_not_equals(){
  assert_not_equals "a string" "a string" "a string should be different from another string"
}
test_obvious_inequality_with_assert_not_equals(){
  assert_not_equals a b
}

```

```output
	Running test_obvious_equality_with_assert_not_equals ... FAILURE
a string should be different from another string
 expected different value than [a string] but was the same
doc:2:test_obvious_equality_with_assert_not_equals()
	Running test_obvious_inequality_with_assert_not_equals ... SUCCESS
```

=== *assert_matches*

    assert_matches <expected-regex> <actual> [message]

Asserts that the string _actual_ matches the regex pattern _expected-regex_.

```test
test_obvious_notmatching_with_assert_matches(){
  assert_matches "a str.*" "another string" "'another string' should not match 'a str.*'"
}
test_obvious_matching_with_assert_matches(){
  assert_matches "a[nN].t{0,1}.*r str.*" "another string"
}

```

```output
	Running test_obvious_matching_with_assert_matches ... SUCCESS
	Running test_obvious_notmatching_with_assert_matches ... FAILURE
'another string' should not match 'a str.*'
 expected regex [a str.*] to match [another string]
doc:2:test_obvious_notmatching_with_assert_matches()
```

=== *assert_not_matches*

    assert_not_matches <unexpected-regex> <actual> [message]

Asserts that the string _actual_ does not match the regex pattern _unexpected-regex_.

```test
test_obvious_matching_with_assert_not_matches(){
  assert_not_matches "a str.*" "a string" "'a string' should not match 'a str.*'"
}
test_obvious_notmatching_with_assert_not_matches(){
  assert_not_matches "a str.*" "another string"
}

```

```output
	Running test_obvious_matching_with_assert_not_matches ... FAILURE
'a string' should not match 'a str.*'
 expected regex [a str.*] should not match but matched [a string]
doc:2:test_obvious_matching_with_assert_not_matches()
	Running test_obvious_notmatching_with_assert_not_matches ... SUCCESS
```

=== *assert_within_delta*

    assert_within_delta <expected num> <actual num> <max delta> [message]

Asserts that the expected num matches the actual num up to a given max delta.
This function only support integers.
Given an expectation of 5 and a delta of 2 this would match 3, 4, 5, 6, and 7:

```test
test_matches_within_delta(){
  assert_within_delta 5 3 2
  assert_within_delta 5 4 2
  assert_within_delta 5 5 2
  assert_within_delta 5 6 2
  assert_within_delta 5 7 2
}
test_does_not_match_within_delta(){
  assert_within_delta 5 2 2
}

```

```output
	Running test_does_not_match_within_delta ... FAILURE
 expected value [5] to match [2] with a maximum delta of [2]
doc:9:test_does_not_match_within_delta()
	Running test_matches_within_delta ... SUCCESS
```

=== *assert_no_diff*

    assert_no_diff <expected> <actual> [message]

Asserts that the content of the file _actual_ does not have any differences to the one _expected_.

```test
test_obvious_notmatching_with_assert_no_diff(){
  assert_no_diff <(echo foo) <(echo bar)
}
test_obvious_matching_with_assert_assert_no_diff(){
  assert_no_diff bash_unit bash_unit
}

```

```output
	Running test_obvious_matching_with_assert_assert_no_diff ... SUCCESS
	Running test_obvious_notmatching_with_assert_no_diff ... FAILURE
 expected 'doc' to be identical to 'doc' but was different
out> 1c1
out> < foo
out> ---
out> > bar
doc:2:test_obvious_notmatching_with_assert_no_diff()
```

== *skip_if* function

    skip_if <condition> <pattern>

If _condition_ is true, will skip all the tests in the current file which match the given _pattern_.

This can be useful when one has tests that are dependent on system environment, for instance:

```test
skip_if "uname | grep Darwin" linux
skip_if "uname | grep Linux" darwin

test_linux_proc_exists() {
  assert "ls /proc/" "there should exist /proc on Linux"
}
test_darwin_proc_does_not_exist() {
  assert_fail "ls /proc/" "there should not exist /proc on Darwin"
}
```

will output, on a Linux system:

```output
	Running test_darwin_proc_does_not_exist ... SKIPPED
	Running test_linux_proc_exists ... SUCCESS
```

== *fake* function

    fake <command> [replacement code]

Fakes _command_ and replaces it with _replacement code_ (if code is specified) for the rest of the execution of your test. If no replacement code is specified, then it replaces command by one that echoes stdin of fake. This may be useful if you need to simulate an environment for you code under test.

For instance:

```test
fake ps echo hello world
ps
```

will output:

```output
hello world
```

We can do the same using _stdin_ of fake:

```test
fake ps << EOF
hello world
EOF
ps
```

```output
hello world
```

ifndef::backend-manpage[]
It has been asked whether using *fake* results in creating actual fakes or stubs or mocks? or may be spies? or may be they are dummies?
The first answer to this question is: it depends. The second is: read this
https://www.google.fr/search?tbm=isch&q=fake%20mock%20stub[great and detailed literature] on this subject.
endif::[]

=== Using stdin

Here is an example, parameterizing fake with its _stdin_ to test that code fails when some process does not run and succeeds otherwise:

```test
code() {
  ps a | grep apache
}

test_code_succeeds_if_apache_runs() {
  fake ps <<EOF
  PID TTY          TIME CMD
13525 pts/7    00:00:01 bash
24162 pts/7    00:00:00 ps
 8387 ?            0:00 /usr/sbin/apache2 -k start
EOF

  assert code "code should succeed when apache is running"
}

test_code_fails_if_apache_does_not_run() {
  fake ps <<EOF
  PID TTY          TIME CMD
13525 pts/7    00:00:01 bash
24162 pts/7    00:00:00 ps
EOF

  assert_fails code "code should fail when apache is not running"
}

```

```output
	Running test_code_fails_if_apache_does_not_run ... SUCCESS
	Running test_code_succeeds_if_apache_runs ... SUCCESS
```

=== Using a function

In a previous example, we faked _ps_ by specifying code inline:

```test
fake ps echo hello world
ps
```

```output
hello world
```

If you need to write more complex code to fake your command, you may abstract this code in a function:

```test
_ps() {
  echo hello world
}
fake ps _ps
ps
```

```output
hello world
```

Be careful however that your _ps function is not exported to sub-processes. It means that, depending on how your code under test works, _ps may not be defined in the context where ps will be called. For instance:

```test
_ps() {
  echo hello world
}
fake ps _ps

bash -c ps
```

```output
environment: line 1: _ps: command not found
```

It depends on your code under test but it is safer to just export functions needed by your fake so that they are available in sub-processes:

```test
_ps() {
  echo hello world
}
export -f _ps
fake ps _ps

bash -c ps
```

```output
hello world
```

*fake* is also limited by the fact that it defines a _bash_ function to
override the actual command. In some context the command can not be
overridden by a function. For instance if your code under test relies on _exec_ to launch _ps_, *fake* will have no effect.

*fake* may also imply strange behaviors from bash_unit when you try to
fake really basic stuff. bash_unit tries to be as much immune to this as
possible but there are some limits. Especially and as surprising as it
might seem, bash allows creating functions named after builtin commands
and bash_unit won't resist that kind of situation. So, for instance, do
not try to fake: `exit`; `local`; `trap`; `eval`; `export`; `if`; `then`; `else`; `fi`; `while`; `do`; `done`; `$`; `echo`; `[` (I know, this is not a builtin but don't).

=== *fake* parameters

*fake* stores parameters given to the fake in the global variable _FAKE_PARAMS_ so that you can use them inside your fake.

It may be useful if you need to adapt the behavior on the given parameters.

It can also help in asserting the values of these parameters ... but this may be quite tricky.

For instance, in our previous code that checks apache is running, we have an issue since our code does not use _ps_ with the appropriate parameters. So we will try to check that parameters given to ps are _ax_.

To do that, the first naive approach would be:

```test
code() {
  ps a | grep apache
}

test_code_gives_ps_appropriate_parameters() {
  _ps() {
    cat <<EOF
  PID TTY          TIME CMD
13525 pts/7    00:00:01 bash
24162 pts/7    00:00:00 ps
 8387 ?            0:00 /usr/sbin/apache2 -k start
EOF
    assert_equals ax "${FAKE_PARAMS[@]}"
  }
  export -f _ps
  fake ps _ps

  code >/dev/null
}
```

This test calls _code_, which calls _ps_, which is actually implemented by __ps_. Since _code_ does not use _ax_ but only _a_ as parameters, this test should fail. But ...

```output
	Running test_code_gives_ps_appropriate_parameters ... SUCCESS
```

The problem here is that _ps_ fail (because of the failed *assert_equals* assertion). But _ps_ is piped with _grep_:

```shell
code() {
  ps a | grep apache
}
```

With bash, the result code of a pipeline equals the result code of the last command of the pipeline. The last command is _grep_ and since grep succeeds, the failure of __ps_ is lost and our test succeeds. We have only succeeded in messing with the test output, nothing more.

An alternative may be to activate bash _pipefail_ option but this may introduce unwanted side effects. We can also simply not output anything in __ps_ so that _grep_ fails:

```shell
code() {
  ps a | grep apache
}

test_code_gives_ps_appropriate_parameters() {
  _ps() {
    assert_equals ax "${FAKE_PARAMS[@]}"
  }
  export -f _ps
  fake ps _ps

  code >/dev/null
}
```

The problem here is that we use a trick to make the code under test fail but the
failure has nothing to do with the actual *assert_equals* failure. This is really
bad, don't do that.

Moreover, *assert_equals* output is captured by _ps_ and this just messes with the display of our test results:

```shell
	Running test_code_gives_ps_appropriate_parameters ...
```

The only correct alternative is for the fake _ps_ to write _FAKE_PARAMS_ in a file descriptor
so that your test can grab them after code execution and assert their value. For instance
by writing to a file:

```test
code() {
  ps a | grep apache
}

test_code_gives_ps_appropriate_parameters() {
  _ps() {
    echo ${FAKE_PARAMS[@]} > /tmp/fake_params
  }
  export -f _ps
  fake ps _ps

  code || true

  assert_equals ax "$(head -n1 /tmp/fake_params)"
}

setup() {
  rm -f /tmp/fake_params
}
```

Here our fake writes to _/tmp/fake_. We delete this file in *setup* to be
sure that we do not get inappropriate data from a previous test. We assert
that the first line of _/tmp/fake_ equals _ax_. Also, note that we know
that _code_ will fail and write this to ignore the error: `code || true`.


```output
	Running test_code_gives_ps_appropriate_parameters ... FAILURE
 expected [ax] but was [a]
doc:14:test_code_gives_ps_appropriate_parameters()
```

We can also compact the fake definition:

```test
code() {
  ps a | grep apache
}

test_code_gives_ps_appropriate_parameters() {
  fake ps 'echo ${FAKE_PARAMS[@]} >/tmp/fake_params'

  code || true

  assert_equals ax "$(head -n1 /tmp/fake_params)"
}

setup() {
  rm -f /tmp/fake_params
}
```

```output
	Running test_code_gives_ps_appropriate_parameters ... FAILURE
 expected [ax] but was [a]
doc:10:test_code_gives_ps_appropriate_parameters()
```

Finally, we can avoid the _/tmp/fake_params_ temporary file by using _coproc_:

```test
code() {
  ps a | grep apache
}

test_get_data_from_fake() {
  #Fasten you seat belt ...
  coproc cat
  exec {test_channel}>&${COPROC[1]}
  fake ps 'echo ${FAKE_PARAMS[@]} >&$test_channel'

  code || true

  assert_equals ax "$(head -n1 <&${COPROC[0]})"
}

```

```output
	Running test_get_data_from_fake ... FAILURE
 expected [ax] but was [a]
doc:13:test_get_data_from_fake()
```