Refactor oslotest base class into fixtures
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Doug Hellmann
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specs/liberty/oslotest-refactor-test-base-class.rst
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specs/liberty/oslotest-refactor-test-base-class.rst
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======================================
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Refactor Test Base Class in oslotest
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======================================
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Include the URL of your launchpad blueprint:
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https://blueprints.launchpad.net/oslo?searchtext=oslotest-refactor
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As a general policy we want to avoid requiring projects to use test
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base classes defined in libraries they do not control. Test fixtures
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are more composable, and easier to test themselves.
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Problem description
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===================
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Copied from :doc:`/specs/policy/test-tools`:
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We originally created oslotest as a place to include the base
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class for all unit tests across all projects, to give the projects
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common behaviors in their test suites. Using a common base class
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is not always possible, however, when applications want to use
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their own base class and test fixture classes in ways that do not
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mix well. Multiple inheritance, in particular, is a problem
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because the order of setup and tear-down for test cases is harder
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to reason about.
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Proposed change
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===============
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1. Provide a fixture to change the ``maxDiff`` attribute of a test
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case, with a default of 10,000 as in BaseTestCase.
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2. Provide a fixture to wrap :class:`fixtures.Timeout` using an environment
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variable to set the actual timeout, based on
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:py:meth:`BaseTestCase._set_timeout`.
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3. Provide a fixture to mock stdout and stderr, based on
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:py:meth:`BaseTestCase._fake_output`.
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4. Provide a fixture to wrap :class:`fixtures.FakeLogger` using an
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environment variable to set the actual timeout, based on
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:py:meth:`BaseTestCase._fake_logs`.
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5. Provide a fixture to create a temporary file with content to
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replicate the features of
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:py:meth:`BaseTestCase.create_tempfiles`. We should use one fixture
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per file, and provide the full path to the resulting file as an
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attribute of the fixture.
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6. Add :class:`DeprecationWarning` to :py:meth:`BaseTestCase.setUp`.
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Alternatives
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------------
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Leave Everything Alone
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~~~~~~~~~~~~~~~~~~~~~~
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Leaving :class:`BaseTestCase` alone risks making it completely
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obsolete as projects drop its use due to issues with multiple
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inheritance.
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Impact on Existing APIs
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-----------------------
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The existing :class:`DeprecationWarning` will not be changed other
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than to add the deprecation warning, so all existing users will
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continue to be able to use it until they move to the new fixtures.
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Security impact
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---------------
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None
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Performance Impact
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------------------
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None
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Configuration Impact
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--------------------
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None
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Developer Impact
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----------------
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Developers will need to create or update their own test base classes
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to use the desired fixtures. The old test case will not be removed for
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at least one cycle, to allow for migration time.
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Testing Impact
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--------------
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We will need unit tests for the new fixtures.
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Implementation
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==============
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Assignee(s)
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-----------
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Primary assignee:
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Doug Hellmann
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Milestones
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----------
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Target Milestone for completion: Liberty-2
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Work Items
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----------
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See "Proposed change" above.
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Incubation
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==========
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N/A
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Adoption
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--------
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N/A
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Library
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-------
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N/A
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Anticipated API Stabilization
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-----------------------------
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N/A
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Documentation Impact
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====================
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Each change will require updates to the API documentation for oslotest.
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Dependencies
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============
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* :doc:`/specs/policy/test-tools`
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References
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==========
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* :doc:`/specs/policy/test-tools`
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.. note::
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This work is licensed under a Creative Commons Attribution 3.0
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Unported License.
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http://creativecommons.org/licenses/by/3.0/legalcode
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@ -55,7 +55,7 @@ Work Items
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----------
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* Deprecate the test base class in oslotest and replicate its features
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in fixtures (see follow-up spec review).
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in fixtures (see :doc:`/specs/liberty/oslotest-refactor-test-base-class`).
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* Deprecate the test base class(es) in oslo.db and replicate their
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features in fixtures (see
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https://blueprints.launchpad.net/oslo.db/+spec/make-db-fixture-public).
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@ -66,6 +66,7 @@ References
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* IRC discussion of issues with oslo.db and nova, starting around
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``2015-02-24T11:36:58`` in
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http://eavesdrop.openstack.org/irclogs/%23openstack-oslo/%23openstack-oslo.2015-02-24.log
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* :doc:`/specs/liberty/oslotest-refactor-test-base-class`
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* https://blueprints.launchpad.net/oslo.db/+spec/make-db-fixture-public
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Revision History
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