Bach Unit Testing Framework

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Bach

Bach is a Bash testing framework, can be used to test scripts that contain dangerous commands like rm -rf /. No surprises, no pain.

Getting Started

Bach Unit Testing Framework is a real unit testing framework. All commands in the PATH environment variable become external dependencies of bash scripts being tested. No commands can be actually executed. In other words, all commands in Bach test cases are dry run. Because that unit tests should verify the behavior of bash scripts, not test commands. Bach Testing Framework also provides APIs to mock commands.

Prerequisites

Installing

Installing Bach Testing Framework is very simple. Download bach.sh to your project, use the source command to import bach.sh.

For example:

source path/to/bach.sh

A complete example

#!/usr/bin/env bash
source bach.sh

test-rm-rf() {
    # Write your test case

    project_log_path=/tmp/project/logs
    rm -rf "$project_log_ptah/" # Typo here!
}
test-rm-rf-assert() {
    # Verify your test case
    rm -rf /   # This is the actual command to run on your host!
               # DO NOT PANIC! By using Bach Testing Framework it won't actually run.
}

test-rm-your-dot-git() {
    # Mock `find` command with certain parameters, will output two directories

    @mock find ~ -type d -name .git === @stdout ~/src/your-awesome-project/.git \
                                                ~/src/code/.git

    # Do it, remove all .git directories
    find ~ -type d -name .git | xargs -- rm -rf
}
test-rm-your-dot-git-assert() {
    # Verify the actual command

    rm -rf ~/src/your-awesome-project/.git ~/src/code/.git
}

See tests/bach-testing-framework.test.sh for more examples.

Write test cases

Unlike the other testing frameworks, A standard test case of Bach is composed of two Bash functions. One is for running tests, the other is for asserting. Bach will run the two functions separately and then compare whether the same sequence of commands will be executed in both functions. The name of a testing function must start with test-, the name of the corresponding asserting function ends with -assert.

For example:

source bach.sh

test-rm-rf() {
    project_log_path=/tmp/project/logs
    sudo rm -rf "$project_log_ptah/" # Typo! 
    # An undefined bash variable is an empty string, which can be a serious problem!
}
test-rm-rf-assert() {
    sudo rm -rf /
}

Bach will run the two functions separately, test-rm-rf and test-rm-rf-assert. In the testing function, test-rm-rf, the final actual command to be executed is sudo rm -rf "/". It’s the same as the asserting function test-rm-rf-assert. So this test case passes.

If Bach does not find the asserting function for a testing function. It will try to use a traditional test method. In this case, the testing function must have a call to assert the APIs. Otherwise, the test case will fail.

For example:

test-single-function-style() {
    declare i=2
    @assert-equals 4 "$((i*2))"
}

If Bach does not find the corresponding asserting function and there is no assertion API call in the testing function, the test case must fail.

If the name of a test case starts with test-ASSERT-FAIL, it means that the asserting result of this test case is reversed. That is, if the asserting result is successful, the test case fails, if the asserting result fails, the test case is successful.

The assertion APIs of Bach Testing Framework:

Mock commands

There are mock APIs in the Bach test framework that can be used to mock commands and scripts.

The Mock APIs:

But it doesn’t allow to mock the following built-in commands in Bach Testing Framework:

Test cases will fail if you attempt to mock these built-in commands. If they are needed in the script under test, we can extract a new function which contains the built-in commands in our scripts, and then use Bach to mock this new function.

Run the actual commands in Bach

In order to make test cases fast, stable, repetitive, and run in random order. We should write unit-testing cases and avoid calling real commands. But Bach also provides a set of APIs for executing real commands.

Bach mocks all commands by default. If it is unavoidable to execute a real command in a test case, Bach provides an API called @real to execute the real command, just put @real at the beginning of commands.

Bach also provides APIs for commonly used commands. The real commands for these APIs are obtained from the system’s PATH environment variable before Bach starts.

These common used APIs are:

command and xargs are a bit special. Bach mocks both commands by default to make the similar behavior of themselves.

In Bach Testing Framework the xargs is a mock function. It’s behavior is similar to the real xargs command if you put -- between xargs and the command. But the commands to be executed by xargs are dry run.

For examples:

test-xargs-no-dash-dash() {
    @mock ls === @stdout foo bar

    ls | xargs -n1 rm -v
}
test-xargs-no-dash-dash-assert() {
    xargs -n1 rm -v
}


test-xargs() {
    @mock ls === @stdout foo bar

    ls | xargs -n1 -- rm -v
}
test-xargs-assert() {
    rm -v foo
    rm -v bar
}


test-xargs-0() {
    @mock ls === @stdout foo bar

    ls | xargs -- rm -v
}
test-xargs-0-assert() {
    rm -v foo bar
}

We can also mock the test command [ ... ]. But it will keep the original behavior if we don’t mock it.

For examples:

test-if-string-is-empty() {
    if [ -n "original behavior" ] # We did not mock it, so this test keeps the original behavior
    then
        It keeps the original behavior by default # We should see this
    else
        It should not be empty
    fi

    @mockfalse [ -n "Non-empty string" ] # We can reverse the test result by mocking it

    if [ -n "Non-empty string" ]
    then
        Non-empty string is not empty # No, we cannot see this
    else
        Non-empty string should not be empty but we reverse its result
    fi
}
test-if-string-is-empty-assert() {
    It keeps the original behavior by default

    Non-empty string should not be empty but we reverse its result
}

# Mocking the test command `[ ... ]` is useful
# when we want to check whether a file with absolute path exists or not
test-a-file-exists() {
    @mocktrue [ -f /etc/an-awesome-config.conf ]
    if [ -f /etc/an-awesome-config.conf ]; then
        Found this awesome config file
    else
        Even though this config file does not exist
    fi
}
test-a-file-exists-assert() {
    Found this awesome config file
}

Configure Bach

There are some environment variables starting with BACH_ for configuring Bach Testing Framework.

Limitation of Bach

Cannot block absolute path command calls

In this case, the OS runs the command directly, and does not interact with Bash(or Shell). Bach cannot intercept such commands. We can wrap this kind of commands in a new function, and then use the @mock API to mock the function.

Prohibit resetting the PATH environment variable

Because Bach wants to intercept all command calls, the PATH is set to read-only to avoid resetting its value.

In the case that PATH needs to be re-assigned, it is recommended to use the declare builtin command in our scripts to avoid errors caused by resetting a read-only environment variable.

Bach is unable to intercept I/O redirection

Bach already support mock functions to read from pipelines. But for the use of operators such as >, >>, the solution is to wrap the redirected command in a function. Another way is to use the sed command to put > or >> in quotation marks, convert the I/O redirected operation to a normal argument.

All command in the pipeline must be mocked

The pipeline commands in Bash are running in sub-processes. Test cases may not be stable if we don’t use @mock API to mock these pipeline commands.

Using unicode character ∅ (empty set) to indicate an empty string

Because there is no way to display an empty string on a terminal. Bach chooses the red empty set symbol ∅ to indicate it’s an empty string.

When we see this red ∅ in test results, it means that the parameter is actually an empty string.

-foobar  ∅
+foobar

Bach APIs

The names of all APIs provided in the Bach testing framework start with @.

@assert-equals

@assert-equals "hello world" "HELLO WORLD"
@assert-equals 1 1

@assert-fail

[[ 1 -eq 3 ]]
@assert-fail

@assert-success

[[ 0 -eq 0 ]]
@assert-success

@comment

Output comments in the test output, but Bach will ignore these comments.

@debug

@die

Terminate the current run immediately

@do-not-panic

Don’t panic.

This API has the following aliases: - donotpanic - dontpanic - do-not-panic - dont-panic - do_not_panic - dont_panic

@do-nothing

Do nothing.

Usually this API is used only in asserting functions to verify that no any commands to be executed in testing functions.

For example:

test-nothing() {
    declare i=9
    if [[ "$i" -eq 0 ]]; then
        do-something
    fi
}
test-nothing-assert() {
    @do-nothing
}

@dryrun

Bach uses @dryrun API to dry run commands by default. But if you want to dry run a mocked command, just put @dryrun in front of this mocked command.

For example:

test-dryrun() {
    @mock ls === @stdout file1 file2 # mock `ls` command
    ls # outputs file1 file2
    @dryrun ls # Dry run `ls` command
}
test-dryrun-assert() {
    @out file1
    @out file2
    ls # @dryrun ls
}

@err

Output error message on stderr console

@ignore

test-ignore-echo() {
    @ignore echo

    echo Updating APT caches
    apt-get update
}
test-ignore-echo-assert() {
    apt-get update
}

@load_function

Loading a function definition from a script.

test-gp() {
    @load_function ./examples/example-functions gp

    gp -f
}
test-gp-assert() {
    git push -f origin master
}

@mock

Mock commands or scripts.

Note:

Use === to split commands and output

For example:

Mock a command that followed by parameters

test-mock-ls() {
    @mock ls file1 === @stdout file2

    ls file1

    ls foo bar
}
test-mock-ls-assert() {
    @out file2 # To list file1, but got file2, It's strange, right?

    ls foo bar
}

Mock commands with complex implementations

For example:

test-mock-foobar() {
  @mock foobar <<<\CMD
    if [[ "$var" -eq 1 ]]; then
      @stdout one
    else
      @stdout others
    fi
CMD

  var=1 foobar
  foobar
}
test-mock-foobar() {
  @out one
  @out others
}

@@mock

Mock the same command multiple times and return different values for each run.

For example:

test-mock-function-multiple-times() {
    @@mock random numbers === @out num 1
    @@mock random numbers === @out num 22
    @@mock random numbers === @out num 333

    random
    random hello
    random numbers
    random numbers
    random numbers
    random numbers
}
test-mock-function-multiple-times-assert() {
    @dryrun random
    @dryrun random hello

    @cat << EOF
num 1
num 22
num 333
num 333
EOF
}

@mockall

Mock many simple commands

@mocktrue

Mock the return code of a command as successful.

@mockfalse

Mock the return code of a command as non-zero value.

@out

Output to the stdout console.

@real

Executing the real command.

@run

Executing the script to be tested.

@setup

Executed at the beginning of the testing functions and the asserting functions.

Note: It doesn’t make sense to run mock in asserting functions, so it’s forbidden to mock any commands in asserting functions.

We cannot mock commands in @setup API.

example:

@setup {
    @echo executing in both the testing function and the asserting function.
}

@setup-assert

Executing at the beginning of all asserting functions.

Note: the test cases will fail if we mock any commands inside @setup-assert

For example:

@setup-assert {
    @echo executing in the asserting functions
}

@setup-test

Executed at the beginning of all testing functions.

This is the only place that allows mock commands outside testing functions.

For example:

@setup-test {
    @echo executing in the testing functions
}

@stderr

Output content to the stderr console, one line per parameter.

@stdout

Output content to the stdout console, one line per parameter.

Learn Bash Programming with Bach

test-learn-bash-no-double-quote-star() {
    @touch bar1 bar2 bar3 "bar*"

    function cleanup() {
        rm -rf $1
    }

    # We want to remove the file "bar*", not the others
    cleanup "bar*"
}
test-learn-bash-no-double-quote-star-assert() {
    # Without double quotes, all bar files are removed!
    rm -rf "bar*" bar1 bar2 bar3
}

test-learn-bash-double-quote-star() {
    @touch bar1 bar2 bar3 "bar*"

    function cleanup() {
        rm -rf "$1"
    }

    # We want to remove the file "bar*", not the others
    cleanup "bar*"
}
test-learn-bash-double-quote-star-assert() {
    # Yes, with double quotes, only the file "bar*" is removed
    rm -rf "bar*"
}

Roadmap

Versioning

The latest version of Bach is 0.5.0, See Bach Releases for more.

Author

Licenses

Bach Testing Framework is dual licensed under:

See LICENSE for more.