Writing Unit Tests

Introduction

Like many software projects, Salt has two broad-based testing approaches -- integration testing and unit testing. While integration testing focuses on the interaction between components in a sandboxed environment, unit testing focuses on the singular implementation of individual functions.

Unit tests should be used specifically to test a function's logic. Unit tests rely on mocking external resources.

While unit tests are good for ensuring consistent results, they are most useful when they do not require more than a few mocks. Effort should be made to mock as many external resources as possible. This effort is encouraged, but not required. Sometimes the isolation provided by completely mocking the external dependencies is not worth the effort of mocking those dependencies.

In these cases, requiring an external library to be installed on the system before running the test file is a useful way to strike this balance. For example, the unit tests for the MySQL execution module require the presence of the MySQL python bindings on the system running the test file before proceeding to run the tests.

Overly detailed mocking can also result in decreased test readability and brittleness as the tests are more likely to fail when the code or its dependencies legitimately change. In these cases, it is better to add dependencies to the test runner dependency state.

Preparing to Write a Unit Test

This guide assumes that your Salt development environment is already configured and that you have a basic understanding of contributing to the Salt codebase. If you're unfamiliar with either of these topics, please refer to the Installing Salt for Development and the Contributing pages, respectively.

This documentation also assumes that you have an understanding of how to run Salt's test suite, including running the unit test subsection, running the unit tests without testing daemons to speed up development wait times, and running a unit test file, class, or individual test.

Best Practices

Unit tests should be written to the following specifications.

What to Test?

Since unit testing focuses on the singular implementation of individual functions, unit tests should be used specifically to test a function's logic. The following guidelines should be followed when writing unit tests for Salt's test suite:

  • Each raise and return statement needs to be independently tested.
  • Isolate testing functionality. Don't rely on the pass or failure of other, separate tests.
  • Test functions should contain only one assertion.
  • Many Salt execution modules are merely wrappers for distribution-specific functionality. If there isn't any logic present in a simple execution module, consider writing an integration test instead of heavily mocking a call to an external dependency.

Mocking Test Data

A reasonable effort needs to be made to mock external resources used in the code being tested, such as APIs, function calls, external data either globally available or passed in through function arguments, file data, etc.

  • Test functions should contain only one assertion and all necessary mock code and data for that assertion.
  • External resources should be mocked in order to "block all of the exits". If a test function fails because something in an external library wasn't mocked properly (or at all), this test is not addressing all of the "exits" a function may experience. We want the Salt code and logic to be tested, specifically.
  • Consider the fragility and longevity of a test. If the test is so tightly coupled to the code being tested, this makes a test unnecessarily fragile.
  • Make sure you are not mocking the function to be tested so vigorously that the test return merely tests the mocked output. The test should always be testing a function's logic.

Mocking Loader Modules

Salt loader modules use a series of globally available dunder variables, __salt__, __opts__, __pillar__, etc. To facilitate testing these modules a mixin class was created, LoaderModuleMockMixin which can be found in tests/support/mixins.py. The reason for the exitance of this class is because, historycally, and because it was easier, one would add these dunder variables directly on the imported module. This however, introduces unexpected behavior when running the full test suite since those attributes would not be removed once we were done testing the module and would therefor leak to other modules being tested with unpredictable results. This is the kind of work that should be defered to mock, and that's exactly what this mixin class does.

As an example, if one needs to specify some options which should be available to the module being tests one should do:

import salt.modules.somemodule as somemodule

class SomeModuleTest(TestCase, LoaderModuleMockMixin):

    def setup_loader_modules(self):
        return {
            somemodule: {
                '__opts__': {'test': True}
            }
        }

Consider this more extensive example from tests/unit/modules/test_libcloud_dns.py:

.. code-block:: python

# Import Python Libs from __future__ import absolute_import

# Import Salt Testing Libs from tests.support.mixins import LoaderModuleMockMixin from tests.support.unit import TestCase, skipIf from tests.support.mock import (

patch, MagicMock, NO_MOCK, NO_MOCK_REASON

) import salt.modules.libcloud_dns as libcloud_dns

class MockDNSDriver(object):
def __init__(self):
pass
def get_mock_driver():
return MockDNSDriver()

@skipIf(NO_MOCK, NO_MOCK_REASON) @patch('salt.modules.libcloud_dns._get_driver',

MagicMock(return_value=MockDNSDriver()))

class LibcloudDnsModuleTestCase(TestCase, LoaderModuleMockMixin):

def setup_loader_modules(self):
module_globals = {
'__salt__': {
'config.option': MagicMock(return_value={
'test': {
'driver': 'test', 'key': '2orgk34kgk34g'

}

})

}

} if libcloud_dns.HAS_LIBCLOUD is False:

module_globals['sys.modules'] = {'libcloud': MagicMock()}

return {libcloud_dns: module_globals}

What happens on the above example is that, we mock a call to __salt__['config.option'] to return the configuration needed for the execution of the tests. Additionally, if the libcloud library is not available, since that's not actually part of whats being tested, we mocked that import by patching sys.modules when tests are running.

Naming Conventions

Test names and docstrings should indicate what functionality is being tested. Test functions are named test_<fcn>_<test-name> where <fcn> is the function being tested and <test-name> describes the raise or return being tested.

Unit tests for salt/.../<module>.py are contained in a file called tests/unit/.../test_<module>.py, e.g. the tests for salt/modules/fib.py are in tests/unit/modules/test_fib.py.

In order for unit tests to get picked up during a run of the unit test suite, each unit test file must be prefixed with test_ and each individual test must be prepended with the test_ naming syntax, as described above.

If a function does not start with test_, then the function acts as a "normal" function and is not considered a testing function. It will not be included in the test run or testing output. The same principle applies to unit test files that do not have the test_*.py naming syntax. This test file naming convention is how the test runner recognizes that a test file contains unit tests.

Imports

Most commonly, the following imports are necessary to create a unit test:

# Import Salt Testing libs
from tests.support.unit import skipIf, TestCase

If you need mock support to your tests, please also import:

from tests.support.mock import NO_MOCK, NO_MOCK_REASON, MagicMock, patch, call

Evaluating Truth

A longer discussion on the types of assertions one can make can be found by reading Python's documentation on unit testing.

Tests Using Mock Objects

In many cases, the purpose of a Salt module is to interact with some external system, whether it be to control a database, manipulate files on a filesystem or something else. In these varied cases, it's necessary to design a unit test which can test the function whilst replacing functions which might actually call out to external systems. One might think of this as "blocking the exits" for code under tests and redirecting the calls to external systems with our own code which produces known results during the duration of the test.

To achieve this behavior, Salt makes heavy use of the MagicMock package.

To understand how one might integrate Mock into writing a unit test for Salt, let's imagine a scenario in which we're testing an execution module that's designed to operate on a database. Furthermore, let's imagine two separate methods, here presented in pseduo-code in an imaginary execution module called 'db.py.

def create_user(username):
    qry = 'CREATE USER {0}'.format(username)
    execute_query(qry)

def execute_query(qry):
    # Connect to a database and actually do the query...

Here, let's imagine that we want to create a unit test for the create_user function. In doing so, we want to avoid any calls out to an external system and so while we are running our unit tests, we want to replace the actual interaction with a database with a function that can capture the parameters sent to it and return pre-defined values. Therefore, our task is clear -- to write a unit test which tests the functionality of create_user while also replacing 'execute_query' with a mocked function.

To begin, we set up the skeleton of our class much like we did before, but with additional imports for MagicMock:

# Import Salt Testing libs
from tests.support.unit import TestCase

# Import Salt execution module to test
from salt.modules import db

# Import Mock libraries
from tests.support.mock import NO_MOCK, NO_MOCK_REASON, MagicMock, patch, call

# Create test case class and inherit from Salt's customized TestCase
# Skip this test case if we don't have access to mock!
@skipIf(NO_MOCK, NO_MOCK_REASON)
class DbTestCase(TestCase):
    def test_create_user(self):
        # First, we replace 'execute_query' with our own mock function
        with patch.object(db, 'execute_query', MagicMock()) as db_exq:

            # Now that the exits are blocked, we can run the function under test.
            db.create_user('testuser')

            # We could now query our mock object to see which calls were made
            # to it.
            ## print db_exq.mock_calls

            # Construct a call object that simulates the way we expected
            # execute_query to have been called.
            expected_call = call('CREATE USER testuser')

            # Compare the expected call with the list of actual calls.  The
            # test will succeed or fail depending on the output of this
            # assertion.
            db_exq.assert_has_calls(expected_call)

Modifying __salt__ In Place

At times, it becomes necessary to make modifications to a module's view of functions in its own __salt__ dictionary. Luckily, this process is quite easy.

Below is an example that uses MagicMock's patch functionality to insert a function into __salt__ that's actually a MagicMock instance.

def show_patch(self):
    with patch.dict(my_module.__salt__,
                    {'function.to_replace': MagicMock()}:
        # From this scope, carry on with testing, with a modified __salt__!

A Simple Example

Let's assume that we're testing a very basic function in an imaginary Salt execution module. Given a module called fib.py that has a function called calculate(num_of_results), which given a num_of_results, produces a list of sequential Fibonacci numbers of that length.

A unit test to test this function might be commonly placed in a file called tests/unit/modules/test_fib.py. The convention is to place unit tests for Salt execution modules in test/unit/modules/ and to name the tests module prefixed with test_*.py.

Tests are grouped around test cases, which are logically grouped sets of tests against a piece of functionality in the tested software. Test cases are created as Python classes in the unit test module. To return to our example, here's how we might write the skeleton for testing fib.py:

# Import Salt Testing libs
from tests.support.unit import TestCase

# Import Salt execution module to test
import salt.modules.fib as fib

# Create test case class and inherit from Salt's customized TestCase
class FibTestCase(TestCase):
    '''
    This class contains a set of functions that test salt.modules.fib.
    '''
    def test_fib(self):
        '''
        To create a unit test, we should prefix the name with `test_' so
        that it's recognized by the test runner.
        '''
        fib_five = (0, 1, 1, 2, 3)
        self.assertEqual(fib.calculate(5), fib_five)

At this point, the test can now be run, either individually or as a part of a full run of the test runner. To ease development, a single test can be executed:

tests/runtests.py -v -n unit.modules.test_fib

This will report the status of the test: success, failure, or error. The -v flag increases output verbosity.

tests/runtests.py -n unit.modules.test_fib -v

To review the results of a particular run, take a note of the log location given in the output for each test:

Logging tests on /var/folders/nl/d809xbq577l3qrbj3ymtpbq80000gn/T/salt-runtests.log

A More Complete Example

Consider the following function from salt/modules/linux_sysctl.py.

def get(name):
    '''
    Return a single sysctl parameter for this minion

    CLI Example:

    .. code-block:: bash

        salt '*' sysctl.get net.ipv4.ip_forward
    '''
    cmd = 'sysctl -n {0}'.format(name)
    out = __salt__['cmd.run'](cmd)
    return out

This function is very simple, comprising only four source lines of code and having only one return statement, so we know only one test is needed. There are also two inputs to the function, the name function argument and the call to __salt__['cmd.run'](), both of which need to be appropriately mocked.

Mocking a function parameter is straightforward, whereas mocking a function call will require, in this case, the use of MagicMock. For added isolation, we will also redefine the __salt__ dictionary such that it only contains 'cmd.run'.

# Import Salt Libs
import salt.modules.linux_sysictl as linux_sysctl

# Import Salt Testing Libs
from tests.support.mixins import LoaderModuleMockMixin
from tests.support.unit import skipIf, TestCase
from tests.support.mock import (
    MagicMock,
    patch,
    NO_MOCK,
    NO_MOCK_REASON
)


@skipIf(NO_MOCK, NO_MOCK_REASON)
class LinuxSysctlTestCase(TestCase, LoaderModuleMockMixin):
    '''
    TestCase for salt.modules.linux_sysctl module
    '''

    def test_get(self):
        '''
        Tests the return of get function
        '''
        mock_cmd = MagicMock(return_value=1)
        with patch.dict(linux_sysctl.__salt__, {'cmd.run': mock_cmd}):
            self.assertEqual(linux_sysctl.get('net.ipv4.ip_forward'), 1)

Since get() has only one raise or return statement and that statement is a success condition, the test function is simply named test_get(). As described, the single function call parameter, name is mocked with net.ipv4.ip_forward and __salt__['cmd.run'] is replaced by a MagicMock function object. We are only interested in the return value of __salt__['cmd.run'], which MagicMock allows us by specifying via return_value=1. Finally, the test itself tests for equality between the return value of get() and the expected return of 1. This assertion is expected to succeed because get() will determine its return value from __salt__['cmd.run'], which we have mocked to return 1.

A Complex Example

Now consider the assign() function from the same salt/modules/linux_sysctl.py source file.

def assign(name, value):
    '''
    Assign a single sysctl parameter for this minion

    CLI Example:

    .. code-block:: bash

        salt '*' sysctl.assign net.ipv4.ip_forward 1
    '''
    value = str(value)
    sysctl_file = '/proc/sys/{0}'.format(name.replace('.', '/'))
    if not os.path.exists(sysctl_file):
        raise CommandExecutionError('sysctl {0} does not exist'.format(name))

    ret = {}
    cmd = 'sysctl -w {0}="{1}"'.format(name, value)
    data = __salt__['cmd.run_all'](cmd)
    out = data['stdout']
    err = data['stderr']

    # Example:
    #    # sysctl -w net.ipv4.tcp_rmem="4096 87380 16777216"
    #    net.ipv4.tcp_rmem = 4096 87380 16777216
    regex = re.compile(r'^{0}\s+=\s+{1}$'.format(re.escape(name),
                                                 re.escape(value)))

    if not regex.match(out) or 'Invalid argument' in str(err):
        if data['retcode'] != 0 and err:
            error = err
        else:
            error = out
        raise CommandExecutionError('sysctl -w failed: {0}'.format(error))
    new_name, new_value = out.split(' = ', 1)
    ret[new_name] = new_value
    return ret

This function contains two raise statements and one return statement, so we know that we will need (at least) three tests. It has two function arguments and many references to non-builtin functions. In the tests below you will see that MagicMock's patch() method may be used as a context manager or as a decorator. When patching the salt dunders however, please use the context manager approach.

There are three test functions, one for each raise and return statement in the source function. Each function is self-contained and contains all and only the mocks and data needed to test the raise or return statement it is concerned with.

# Import Salt Libs
import salt.modules.linux_sysctl as linux_sysctl
from salt.exceptions import CommandExecutionError

# Import Salt Testing Libs
from tests.support.mixins import LoaderModuleMockMixin
from tests.support.unit import skipIf, TestCase
from tests.support.mock import (
    MagicMock,
    patch,
    NO_MOCK,
    NO_MOCK_REASON
)


@skipIf(NO_MOCK, NO_MOCK_REASON)
class LinuxSysctlTestCase(TestCase, LoaderModuleMockMixin):
    '''
    TestCase for salt.modules.linux_sysctl module
    '''

    @patch('os.path.exists', MagicMock(return_value=False))
    def test_assign_proc_sys_failed(self):
        '''
        Tests if /proc/sys/<kernel-subsystem> exists or not
        '''
        cmd = {'pid': 1337, 'retcode': 0, 'stderr': '',
               'stdout': 'net.ipv4.ip_forward = 1'}
        mock_cmd = MagicMock(return_value=cmd)
        with patch.dict(linux_sysctl.__salt__, {'cmd.run_all': mock_cmd}):
            self.assertRaises(CommandExecutionError,
                              linux_sysctl.assign,
                              'net.ipv4.ip_forward', 1)

    @patch('os.path.exists', MagicMock(return_value=True))
    def test_assign_cmd_failed(self):
        '''
        Tests if the assignment was successful or not
        '''
        cmd = {'pid': 1337, 'retcode': 0, 'stderr':
               'sysctl: setting key "net.ipv4.ip_forward": Invalid argument',
               'stdout': 'net.ipv4.ip_forward = backward'}
        mock_cmd = MagicMock(return_value=cmd)
        with patch.dict(linux_sysctl.__salt__, {'cmd.run_all': mock_cmd}):
            self.assertRaises(CommandExecutionError,
                              linux_sysctl.assign,
                              'net.ipv4.ip_forward', 'backward')

    @patch('os.path.exists', MagicMock(return_value=True))
    def test_assign_success(self):
        '''
        Tests the return of successful assign function
        '''
        cmd = {'pid': 1337, 'retcode': 0, 'stderr': '',
               'stdout': 'net.ipv4.ip_forward = 1'}
        ret = {'net.ipv4.ip_forward': '1'}
        mock_cmd = MagicMock(return_value=cmd)
        with patch.dict(linux_sysctl.__salt__, {'cmd.run_all': mock_cmd}):
            self.assertEqual(linux_sysctl.assign(
                'net.ipv4.ip_forward', 1), ret)