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The Importance of Testing
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=========================
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Reliability is a critical success factor for any Version Control System.
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We want Bazaar to be highly reliable across multiple platforms while
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evolving over time to meet the needs of its community.
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In a nutshell, this is what we expect and encourage:
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* New functionality should have test cases. Preferably write the
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test before writing the code.
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In general, you can test at either the command-line level or the
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internal API level. See `Writing tests`_ below for more detail.
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* Try to practice Test-Driven Development: before fixing a bug, write a
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test case so that it does not regress. Similarly for adding a new
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feature: write a test case for a small version of the new feature before
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starting on the code itself. Check the test fails on the old code, then
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add the feature or fix and check it passes.
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By doing these things, the Bazaar team gets increased confidence that
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changes do what they claim to do, whether provided by the core team or
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by community members. Equally importantly, we can be surer that changes
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down the track do not break new features or bug fixes that you are
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As of May 2008, Bazaar ships with a test suite containing over 12000 tests
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and growing. We are proud of it and want to remain so. As community
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members, we all benefit from it. Would you trust version control on
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your project to a product *without* a test suite like Bazaar has?
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Running the Test Suite
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======================
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Currently, bzr selftest is used to invoke tests.
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You can provide a pattern argument to run a subset. For example,
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to run just the blackbox tests, run::
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./bzr selftest -v blackbox
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To skip a particular test (or set of tests), use the --exclude option
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(shorthand -x) like so::
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./bzr selftest -v -x blackbox
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To ensure that all tests are being run and succeeding, you can use the
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--strict option which will fail if there are any missing features or known
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./bzr selftest --strict
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To list tests without running them, use the --list-only option like so::
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./bzr selftest --list-only
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This option can be combined with other selftest options (like -x) and
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filter patterns to understand their effect.
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Once you understand how to create a list of tests, you can use the --load-list
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option to run only a restricted set of tests that you kept in a file, one test
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id by line. Keep in mind that this will never be sufficient to validate your
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modifications, you still need to run the full test suite for that, but using it
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can help in some cases (like running only the failed tests for some time)::
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./bzr selftest -- load-list my_failing_tests
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This option can also be combined with other selftest options, including
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patterns. It has some drawbacks though, the list can become out of date pretty
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quick when doing Test Driven Development.
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To address this concern, there is another way to run a restricted set of tests:
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the --starting-with option will run only the tests whose name starts with the
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specified string. It will also avoid loading the other tests and as a
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consequence starts running your tests quicker::
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./bzr selftest --starting-with bzrlib.blackbox
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This option can be combined with all the other selftest options including
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--load-list. The later is rarely used but allows to run a subset of a list of
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failing tests for example.
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Test suite debug flags
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----------------------
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Similar to the global ``-Dfoo`` debug options, bzr selftest accepts
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``-E=foo`` debug flags. These flags are:
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:allow_debug: do *not* clear the global debug flags when running a test.
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This can provide useful logging to help debug test failures when used
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with e.g. ``bzr -Dhpss selftest -E=allow_debug``
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Where should I put a new test?
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------------------------------
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Bzrlib's tests are organised by the type of test. Most of the tests in
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bzr's test suite belong to one of these categories:
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- Blackbox (UI) tests
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- Per-implementation tests
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A quick description of these test types and where they belong in bzrlib's
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source follows. Not all tests fall neatly into one of these categories;
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in those cases use your judgement.
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Unit tests make up the bulk of our test suite. These are tests that are
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focused on exercising a single, specific unit of the code as directly
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as possible. Each unit test is generally fairly short and runs very
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They are found in ``bzrlib/tests/test_*.py``. So in general tests should
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be placed in a file named test_FOO.py where FOO is the logical thing under
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For example, tests for merge3 in bzrlib belong in bzrlib/tests/test_merge3.py.
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See bzrlib/tests/test_sampler.py for a template test script.
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Tests can be written for the UI or for individual areas of the library.
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Choose whichever is appropriate: if adding a new command, or a new command
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option, then you should be writing a UI test. If you are both adding UI
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functionality and library functionality, you will want to write tests for
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both the UI and the core behaviours. We call UI tests 'blackbox' tests
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and they belong in ``bzrlib/tests/blackbox/*.py``.
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When writing blackbox tests please honour the following conventions:
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1. Place the tests for the command 'name' in
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bzrlib/tests/blackbox/test_name.py. This makes it easy for developers
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to locate the test script for a faulty command.
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2. Use the 'self.run_bzr("name")' utility function to invoke the command
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rather than running bzr in a subprocess or invoking the
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cmd_object.run() method directly. This is a lot faster than
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subprocesses and generates the same logging output as running it in a
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subprocess (which invoking the method directly does not).
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3. Only test the one command in a single test script. Use the bzrlib
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library when setting up tests and when evaluating the side-effects of
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the command. We do this so that the library api has continual pressure
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on it to be as functional as the command line in a simple manner, and
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to isolate knock-on effects throughout the blackbox test suite when a
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command changes its name or signature. Ideally only the tests for a
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given command are affected when a given command is changed.
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4. If you have a test which does actually require running bzr in a
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subprocess you can use ``run_bzr_subprocess``. By default the spawned
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process will not load plugins unless ``--allow-plugins`` is supplied.
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Per-implementation tests
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~~~~~~~~~~~~~~~~~~~~~~~~
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Per-implementation tests are tests that are defined once and then run
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against multiple implementations of an interface. For example,
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``test_transport_implementations.py`` defines tests that all Transport
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implementations (local filesystem, HTTP, and so on) must pass.
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They are found in ``bzrlib/tests/*_implementations/test_*.py``,
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``bzrlib/tests/per_*/*.py``, and
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``bzrlib/tests/test_*_implementations.py``.
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These are really a sub-category of unit tests, but an important one.
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We make selective use of doctests__. In general they should provide
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*examples* within the API documentation which can incidentally be tested. We
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don't try to test every important case using doctests |--| regular Python
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tests are generally a better solution. That is, we just use doctests to
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make our documentation testable, rather than as a way to make tests.
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Most of these are in ``bzrlib/doc/api``. More additions are welcome.
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__ http://docs.python.org/lib/module-doctest.html
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In our enhancements to unittest we allow for some addition results beyond
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just success or failure.
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If a test can't be run, it can say that it's skipped by raising a special
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exception. This is typically used in parameterized tests |--| for example
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if a transport doesn't support setting permissions, we'll skip the tests
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that relating to that. ::
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return self.branch_format.initialize(repo.bzrdir)
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except errors.UninitializableFormat:
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raise tests.TestSkipped('Uninitializable branch format')
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Raising TestSkipped is a good idea when you want to make it clear that the
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test was not run, rather than just returning which makes it look as if it
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Several different cases are distinguished:
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Generic skip; the only type that was present up to bzr 0.18.
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The test doesn't apply to the parameters with which it was run.
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This is typically used when the test is being applied to all
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implementations of an interface, but some aspects of the interface
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are optional and not present in particular concrete
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implementations. (Some tests that should raise this currently
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either silently return or raise TestSkipped.) Another option is
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to use more precise parameterization to avoid generating the test
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The test can't be run because a dependency (typically a Python
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library) is not available in the test environment. These
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are in general things that the person running the test could fix
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by installing the library. It's OK if some of these occur when
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an end user runs the tests or if we're specifically testing in a
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limited environment, but a full test should never see them.
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See `Test feature dependencies`_ below.
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The test exists but is known to fail, for example this might be
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appropriate to raise if you've committed a test for a bug but not
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the fix for it, or if something works on Unix but not on Windows.
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Raising this allows you to distinguish these failures from the
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ones that are not expected to fail. If the test would fail
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because of something we don't expect or intend to fix,
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KnownFailure is not appropriate, and TestNotApplicable might be
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KnownFailure should be used with care as we don't want a
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proliferation of quietly broken tests.
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We plan to support three modes for running the test suite to control the
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interpretation of these results. Strict mode is for use in situations
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like merges to the mainline and releases where we want to make sure that
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everything that can be tested has been tested. Lax mode is for use by
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developers who want to temporarily tolerate some known failures. The
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default behaviour is obtained by ``bzr selftest`` with no options, and
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also (if possible) by running under another unittest harness.
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======================= ======= ======= ========
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result strict default lax
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======================= ======= ======= ========
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TestSkipped pass pass pass
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TestNotApplicable pass pass pass
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UnavailableFeature fail pass pass
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KnownFailure fail pass pass
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======================= ======= ======= ========
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Test feature dependencies
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-------------------------
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Writing tests that require a feature
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Rather than manually checking the environment in each test, a test class
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can declare its dependence on some test features. The feature objects are
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checked only once for each run of the whole test suite.
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(For historical reasons, as of May 2007 many cases that should depend on
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features currently raise TestSkipped.)
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class TestStrace(TestCaseWithTransport):
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_test_needs_features = [StraceFeature]
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This means all tests in this class need the feature. If the feature is
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not available the test will be skipped using UnavailableFeature.
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Individual tests can also require a feature using the ``requireFeature``
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self.requireFeature(StraceFeature)
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Features already defined in bzrlib.tests include:
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- UnicodeFilenameFeature,
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- FTPServerFeature, and
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- CaseInsensitiveFilesystemFeature.
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Defining a new feature that tests can require
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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New features for use with ``_test_needs_features`` or ``requireFeature``
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are defined by subclassing ``bzrlib.tests.Feature`` and overriding the
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``_probe`` and ``feature_name`` methods. For example::
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class _SymlinkFeature(Feature):
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return osutils.has_symlinks()
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def feature_name(self):
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SymlinkFeature = _SymlinkFeature()
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Testing exceptions and errors
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-----------------------------
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It's important to test handling of errors and exceptions. Because this
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code is often not hit in ad-hoc testing it can often have hidden bugs --
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it's particularly common to get NameError because the exception code
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references a variable that has since been renamed.
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.. TODO: Something about how to provoke errors in the right way?
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In general we want to test errors at two levels:
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1. A test in ``test_errors.py`` checking that when the exception object is
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constructed with known parameters it produces an expected string form.
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This guards against mistakes in writing the format string, or in the
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``str`` representations of its parameters. There should be one for
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each exception class.
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2. Tests that when an api is called in a particular situation, it raises
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an error of the expected class. You should typically use
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``assertRaises``, which in the Bazaar test suite returns the exception
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object to allow you to examine its parameters.
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In some cases blackbox tests will also want to check error reporting. But
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it can be difficult to provoke every error through the commandline
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interface, so those tests are only done as needed |--| eg in response to a
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particular bug or if the error is reported in an unusual way(?) Blackbox
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tests should mostly be testing how the command-line interface works, so
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should only test errors if there is something particular to the cli in how
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they're displayed or handled.
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The Python ``warnings`` module is used to indicate a non-fatal code
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problem. Code that's expected to raise a warning can be tested through
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The test suite can be run with ``-Werror`` to check no unexpected errors
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However, warnings should be used with discretion. It's not an appropriate
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way to give messages to the user, because the warning is normally shown
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only once per source line that causes the problem. You should also think
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about whether the warning is serious enought that it should be visible to
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users who may not be able to fix it.
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Interface implementation testing and test scenarios
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---------------------------------------------------
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There are several cases in Bazaar of multiple implementations of a common
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conceptual interface. ("Conceptual" because it's not necessary for all
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the implementations to share a base class, though they often do.)
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Examples include transports and the working tree, branch and repository
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In these cases we want to make sure that every implementation correctly
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fulfils the interface requirements. For example, every Transport should
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support the ``has()`` and ``get()`` and ``clone()`` methods. We have a
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sub-suite of tests in ``test_transport_implementations``. (Most
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per-implementation tests are in submodules of ``bzrlib.tests``, but not
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the transport tests at the moment.)
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These tests are repeated for each registered Transport, by generating a
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new TestCase instance for the cross product of test methods and transport
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implementations. As each test runs, it has ``transport_class`` and
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``transport_server`` set to the class it should test. Most tests don't
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access these directly, but rather use ``self.get_transport`` which returns
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a transport of the appropriate type.
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The goal is to run per-implementation only the tests that relate to that
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particular interface. Sometimes we discover a bug elsewhere that happens
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with only one particular transport. Once it's isolated, we can consider
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whether a test should be added for that particular implementation,
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or for all implementations of the interface.
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The multiplication of tests for different implementations is normally
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accomplished by overriding the ``load_tests`` function used to load tests
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from a module. This function typically loads all the tests, then applies
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a TestProviderAdapter to them, which generates a longer suite containing
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all the test variations.
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See also `Per-implementation tests`_ (above).
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Some utilities are provided for generating variations of tests. This can
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be used for per-implementation tests, or other cases where the same test
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code needs to run several times on different scenarios.
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The general approach is to define a class that provides test methods,
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which depend on attributes of the test object being pre-set with the
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values to which the test should be applied. The test suite should then
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also provide a list of scenarios in which to run the tests.
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Typically ``multiply_tests_from_modules`` should be called from the test
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module's ``load_tests`` function.
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We have a rich collection of tools to support writing tests. Please use
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them in preference to ad-hoc solutions as they provide portability and
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performance benefits.
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TestCase and its subclasses
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~~~~~~~~~~~~~~~~~~~~~~~~~~~
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The ``bzrlib.tests`` module defines many TestCase classes to help you
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A base TestCase that extends the Python standard library's
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TestCase in several ways. It adds more assertion methods (e.g.
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``assertContainsRe``), ``addCleanup``, and other features (see its API
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docs for details). It also has a ``setUp`` that makes sure that
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global state like registered hooks and loggers won't interfere with
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your test. All tests should use this base class (whether directly or
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TestCaseWithMemoryTransport
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Extends TestCase and adds methods like ``get_transport``,
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``make_branch`` and ``make_branch_builder``. The files created are
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stored in a MemoryTransport that is discarded at the end of the test.
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This class is good for tests that need to make branches or use
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transports, but that don't require storing things on disk. All tests
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that create bzrdirs should use this base class (either directly or via
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a subclass) as it ensures that the test won't accidentally operate on
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real branches in your filesystem.
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Extends TestCaseWithMemoryTransport. For tests that really do need
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files to be stored on disk, e.g. because a subprocess uses a file, or
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for testing functionality that accesses the filesystem directly rather
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than via the Transport layer (such as dirstate).
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TestCaseWithTransport
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Extends TestCaseInTempDir. Provides ``get_url`` and
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``get_readonly_url`` facilities. Subclasses can control the
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transports used by setting ``vfs_transport_factory``,
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``transport_server`` and/or ``transport_readonly_server``.
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See the API docs for more details.
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When writing a test for a feature, it is often necessary to set up a
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branch with a certain history. The ``BranchBuilder`` interface allows the
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creation of test branches in a quick and easy manner. Here's a sample
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builder = self.make_branch_builder('relpath')
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builder.build_commit()
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builder.build_commit()
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builder.build_commit()
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branch = builder.get_branch()
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``make_branch_builder`` is a method of ``TestCaseWithMemoryTransport``.
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Note that many current tests create test branches by inheriting from
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``TestCaseWithTransport`` and using the ``make_branch_and_tree`` helper to
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give them a ``WorkingTree`` that they can commit to. However, using the
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newer ``make_branch_builder`` helper is preferred, because it can build
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the changes in memory, rather than on disk. Tests that are explictly
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testing how we work with disk objects should, of course, use a real
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Please see bzrlib.branchbuilder for more details.
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If you're going to examine the commit timestamps e.g. in a test for log
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output, you should set the timestamp on the tree, rather than using fuzzy
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The ``TreeBuilder`` interface allows the construction of arbitrary trees
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with a declarative interface. A sample session might look like::
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tree = self.make_branch_and_tree('path')
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builder = TreeBuilder()
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builder.start_tree(tree)
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builder.build(['foo', "bar/", "bar/file"])
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tree.commit('commit the tree')
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builder.finish_tree()
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Usually a test will create a tree using ``make_branch_and_memory_tree`` (a
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method of ``TestCaseWithMemoryTransport``) or ``make_branch_and_tree`` (a
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method of ``TestCaseWithTransport``).
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Please see bzrlib.treebuilder for more details.
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.. |--| unicode:: U+2014
added
removed
doc/developers/testing.txt
