qubes.tests – Writing tests for qubes

Writing tests is very important for ensuring quality of code that is delivered. Given test case may check for variety of conditions, but they generally fall inside those two categories of conformance tests:

  • Unit tests: these test smallest units of code, probably methods of functions, or even combination of arguments for one specific method.
  • Integration tests: these test interworking of units.

We are interested in both categories.

There is also distinguished category of regression tests (both unit- and integration-level), which are included because they check for specific bugs that were fixed in the past and should not happen in the future. Those should be accompanied with reference to closed ticked that describes the bug.

Qubes’ tests are written using unittest module from Python Standard Library for both unit test and integration tests.

Test case organisation

Every module (like qubes.vm.qubesvm) should have its companion (like qubes.tests.vm.qubesvm). Packages __init__.py files should be accompanied by init.py inside respective directory under tests/. Inside tests module there should be one qubes.tests.QubesTestCase class for each class in main module plus one class for functions and global variables. qubes.tests.QubesTestCase classes should be named TC_xx_ClassName, where xx is two-digit number. Test functions should be named test_xxx_test_name, where xxx is three-digit number. You may introduce some structure of your choice in this number.

Integration tests for Qubes core features are stored in tests/integ/ directory. Additional tests may be loaded from other packages (see extra test loader below). Those tests are run only on real Qubes system and are not suitable for running in VM or in Travis. Test classes of this category inherit from qubes.tests.SystemTestCase.

Writing tests

First of all, testing is art, not science. Testing is not panaceum and won’t solve all of your problems. Rules given in this guide and elsewhere should be followed, but shouldn’t be worshipped.

Test can be divided into three phases. The first part is setup phase. In this part you should arrange for a test condition to occur. You intentionally put system under test in some specific state. Phase two is executing test condition – for example you check some variable for equality or expect that some exception is raised. Phase three is responsible for returning a verdict. This is largely done by the framework.

When writing test, you should think about order of execution. This is the reason of numbers in names of the classes and test methods. Tests should be written bottom-to-top, that is, test setups that are ran later may depend on features that are tested after but not the other way around. This is important, because when encountering failure we expect the reason happen before, and not after failure occured. Therefore, when encountering multiple errors, we may instantly focus on fixing the first one and not wondering if any later problems may be relevant or not. Some people also like to enable unittest.TestResult.failfast feature, which stops on the first failed test – with wrong order this messes up their workflow.

Test should fail for one reason only and test one specific issue. This does not mean that you can use one .assert* method per test_ function: for example when testing one regular expression you are welcome to test many valid and/or invalid inputs, especcialy when test setup is complicated. However, if you encounter problems during setup phase, you should skip the test, and not fail it. This also aids interpretation of results.

You may, when it makes sense, manipulate private members of classes under tests. This violates one of the founding principles of object-oriented programming, but may be required to write tests in correct order if your class provides public methods with circular dependencies. For example containers may check if added item is already in container, but you can’t test __contains__ method without something already inside. Don’t forget to test the other method later.

Special Qubes-specific considerations

Events

qubes.tests.QubesTestCase provides convenient methods for checking if event fired or not: qubes.tests.QubesTestCase.assertEventFired() and qubes.tests.QubesTestCase.assertEventNotFired(). These require that emitter is subclass of qubes.tests.TestEmitter. You may instantiate it directly:

import qubes.tests

class TC_10_SomeClass(qubes.tests.QubesTestCase):
    def test_000_event(self):
        emitter = qubes.tests.TestEmitter()
        emitter.fire_event('did-fire')
        self.assertEventFired(emitter, 'did-fire')

If you need to snoop specific class (which already is a child of qubes.events.Emitter, possibly indirect), you can define derivative class which uses qubes.tests.TestEmitter as mix-in:

import qubes
import qubes.tests

class TestHolder(qubes.tests.TestEmitter, qubes.PropertyHolder):
    pass

class TC_20_PropertyHolder(qubes.tests.QubesTestCase):
    def test_000_event(self):
        emitter = TestHolder()
        self.assertEventNotFired(emitter, 'did-not-fire')

Dom0

Qubes is a complex piece of software and depends on number other complex pieces, notably VM hypervisor or some other isolation provider. Not everything may be testable under all conditions. Some tests (mainly unit tests) are expected to run during compilation, but many tests (probably all of the integration tests and more) can run only inside already deployed Qubes installation. There is special decorator, qubes.tests.skipUnlessDom0() which causes test (or even entire class) to be skipped outside dom0. Use it freely:

import qubes.tests

class TC_30_SomeClass(qubes.tests.QubesTestCase):
    @qubes.tests.skipUnlessDom0
    def test_000_inside_dom0(self):
        # this is skipped outside dom0
        pass

@qubes.tests.skipUnlessDom0
class TC_31_SomeOtherClass(qubes.tests.QubesTestCase):
    # all tests in this class are skipped
    pass

VM tests

Some integration tests verifies not only dom0 part of the system, but also VM part. In those cases, it makes sense to iterate them for different templates. Additionally, list of the templates can be dynamic (different templates installed, only some considered for testing etc). This can be achieved by creating a mixin class with the actual tests (a class inheriting just from object, instead of qubes.tests.SystemTestCase or unittest.TestCase) and then create actual test classes dynamically using qubes.tests.create_testcases_for_templates(). Test classes created this way will have template set to the template name under test and also this template will be set as the default template during the test execution. The function takes a test class name prefix (template name will be appended to it after ‘_’ separator), a classes to inherit from (in most cases the just created mixin and qubes.tests.SystemTestCase) and a current module object (use sys.modules[__name__]). The function will return created test classes but also add them to the appropriate module (pointed by the module parameter). This should be done in two cases:

  • load_tests() function - when test loader request list of tests
  • on module import time, using a wrapper qubes.tests.maybe_create_testcases_on_import() (will call the function only if explicit list of templates is given, to avoid loading qubes.xml when just importing the module)

An example boilerplate looks like this:

def create_testcases_for_templates():
    return qubes.tests.create_testcases_for_templates('TC_00_AppVM',
        TC_00_AppVMMixin, qubes.tests.SystemTestCase,
        module=sys.modules[__name__])

def load_tests(loader, tests, pattern):
    tests.addTests(loader.loadTestsFromNames(
        create_testcases_for_templates()))
    return tests

qubes.tests.maybe_create_testcases_on_import(create_testcases_for_templates)

This will by default create tests for all the templates installed in the system. Additionally, it is possible to control this process using environment variables:

  • QUBES_TEST_TEMPLATES - space separated list of templates to test
  • QUBES_TEST_LOAD_ALL - create tests for all the templates (by inspecting the qubes.xml file), even at module import time

This is dynamic test creation is intentionally made compatible with Nose2 test runner and its load_tests protocol implementation.

Extra tests

Most tests live in this package, but it is also possible to store tests in other packages while still using infrastructure provided here and include them in the common test run. Loading extra tests is implemented in qubes.tests.extra. To write test to be loaded this way, you need to create test class(es) as usual. You can also use helper class qubes.tests.extra.ExtraTestCase (instead of qubes.tests.SystemTestCase) which provide few convenient functions and hide usage of asyncio for simple cases (like vm.start(), vm.run()).

The next step is to register the test class(es). You need to do this by defining entry point for your package. There are two groups:

  • qubes.tests.extra - for general tests (called once)
  • qubes.tests.extra.for_template - for per-VM tests (called for each template under test)

As a name in the group, choose something unique, preferably package name. An object reference should point at the function that returns a list of test classes.

Example setup.py:

from setuptools import setup

setup(
    name='splitgpg',
    version='1.0',
    packages=['splitgpg'],
    entry_points={
        'qubes.tests.extra.for_template':
            'splitgpg = splitgpg.tests:list_tests',
    }
)

The test loading process can be additionally controlled with environment variables:

  • QUBES_TEST_EXTRA_INCLUDE - space separated list of tests to include (named by a name in an entry point, splitgpg in the above example); if defined, only those extra tests will be loaded
  • QUBES_TEST_EXTRA_EXCLUDE - space separated list of tests to exclude

Module contents