Trove Unit Tests¶
Mock Object Library¶
Trove unit tests make a frequent use of the Python Mock library. This library lets the caller replace (“mock”) parts of the system under test with mock objects and make assertions about how they have been used. 1
The Problem of Dangling Mocks¶
Often one needs to mock global functions in shared system modules. The caller must restore the original state of the module after it is no longer required.
Dangling mock objects in global modules (mocked members of imported modules that never get restored) have been causing various transient failures in the unit test suite.
The main issues posed by dangling mock objects include:
- Such object references propagate across the entire test suite. Any caller may be hit by a non-functional - or worse - crippled module member because some other (potentially totally unrelated) test case failed to restore it. - Dangling mock references shared across different test modules may lead to unexpected results/behavior in multi-threaded environments. One example could be a test case failing because a mock got called multiple times from unrelated modules.
Such issues are likely to exhibit transient random behavior depending on the runtime environment, making them difficult to debug.
There are several possible strategies available for dealing with dangling mock objects (see the section on recommended patterns). Further information is available in 1, 2, 3.
Dangling Mock Detector¶
All Trove unit tests should extend ‘trove_testtools.TestCase’. It is a subclass of ‘testtools.TestCase’ which automatically checks for dangling mock objects at each test class teardown. It marks the tests as failed and reports the leaked reference if it finds any.
Writing Unit Tests¶
Trove has some legacy unit test code for all the components which is not recommended to follow. Use the suggested approaches below.
Writing Unit Tests for Trove API¶
For trove-api unit test, we use real database (sqlite).
Set up trove database in
from trove.tests.unittests.util import util @classmethod def setUpClass(cls): util.init_db()
and clean up the database in the method
from trove.tests.unittests.util import util @classmethod def tearDownClass(cls): util.cleanup_db()
Insert some data in
setUpClass in order to run the tests.
Trove sends notifications for various operations which communicates with
the message queue service. In unit test, this is also mocked and usually
called in the
from trove.tests.unittests import trove_testtools def setUp(self): trove_testtools.patch_notifier(self)
Look at an example in
Run Unit Test¶
Run all the unit tests in one command:
tox -e py39
Run all the tests of a specific test class:
tox -e py39 -- trove.tests.unittests.instance.test_service.TestInstanceController
Run a single test case:
tox -e py39 -- trove.tests.unittests.instance.test_service.TestInstanceController.test_create_multiple_versions
Mock Guide: https://docs.python.org/3/library/unittest.mock.html
Python Mock Gotchas: http://alexmarandon.com/articles/python_mock_gotchas/
Mocking Mistakes: http://engineroom.trackmaven.com/blog/mocking-mistakes/