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.

Preparing to Write a Unit Test

This guide assumes you've followed the directions for setting up salt testing.

Unit tests should be written to the following specifications:

  • All the tests for a specific module at salt/.../<module>.py need to be contained in a file called tests/unit/.../<module>_test.py, e.g. the tests for salt/modules/fib.py need to be contained in a file called tests/unit/modules/fib_test.py.
  • The tests within tests/unit/modules/fib_test.py file must be member functions of a class which subclasses salttesting.Testcase
  • Each external resource used in the code to be tested, such as function calls, external data either globally available or passed in through the function arguments, file data, etc. needs to be mocked.
  • Each raise and return statement of the code to be tested needs to be separately and independently tested.
  • Test functions should contain only one test and contain all necessary mock data and mock code for that test.
  • Test functions should be named test_<fcn>_<test-name> where <fcn> is the name of the function being tested and <test-name> describes which raise or return within the function is being tested and whether that raise or return statement is considered a success or a failure condition.

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

# Import Salt Testing libs
from salttesting import skipIf, TestCase
from salttesting.helpers import ensure_in_syspath

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

from salttesting.mock import NO_MOCK, NO_MOCK_REASON, MagicMock, patch, call

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/fib_test.py. The convention is to place unit tests for Salt execution modules in test/unit/modules/ and to name the tests module suffixed 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 salttesting import TestCase

# Import Salt execution module to test
from salt.modules import 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 -n unit.modules.fib_test

This will produce output indicating the success or failure of the tests in given test case. For more detailed results, one can also include a flag to increase verbosity:

tests/runtests.py -n unit.modules.fib_test -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

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 very 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 many other examples. 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 salttesting import TestCase

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

# NEW! -- Import Mock libraries
from salttesting.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
        db.execute_query = MagicMock()

        # 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.execute_query.mock_calls

        '''
        We want to test to ensure that the correct query was formed.  This
        is a contrived example, just designed to illustrate the concepts at
        hand.

        We're going to first construct a call() object that represents the
        way we expect our mocked execute_query() function to have been
        called.  Then, we'll examine the list of calls that were actually
        made to to execute_function().

        By comparing our expected call to execute_query() with
        create_user()'s call to execute_query(), we can determine the
        success or failure of our unit test.
        '''

        expected_call = call('CREATE USER testuser')

        # Do the comparison! Will assert False if execute_query() was not
        # called with the given call

        db.execute_query.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 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
from salt.modules import linux_sysctl

# Import Salt Testing Libs
from salttesting import skipIf, TestCase
from salttesting.helpers import ensure_in_syspath
from salttesting.mock import (
    MagicMock,
    patch,
    NO_MOCK,
    NO_MOCK_REASON
)

ensure_in_syspath('../../')

# Globals
linux_sysctl.__salt__ = {}


@skipIf(NO_MOCK, NO_MOCK_REASON)
class LinuxSysctlTestCase(TestCase):
    '''
    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)


if __name__ == '__main__':
    from integration import run_tests
    run_tests(LinuxSysctlTestCase, needs_daemon=False)

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 to be specified 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.

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
from salt.modules import linux_sysctl
from salt.exceptions import CommandExecutionError

# Import Salt Testing Libs
from salttesting import skipIf, TestCase
from salttesting.helpers import ensure_in_syspath
from salttesting.mock import (
    MagicMock,
    patch,
    NO_MOCK,
    NO_MOCK_REASON
)

ensure_in_syspath('../../')

# Globals
linux_sysctl.__salt__ = {}


@skipIf(NO_MOCK, NO_MOCK_REASON)
class LinuxSysctlTestCase(TestCase):
    '''
    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)

if __name__ == '__main__':
    from integration import run_tests
    run_tests(LinuxSysctlTestCase, needs_daemon=False)

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