6
The Importance of Testing
7
=========================
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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 September 2009, Bazaar ships with a test suite containing over
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23,000 tests and growing. We are proud of it and want to remain so. As
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community members, we all benefit from it. Would you trust version control
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on 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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``bzrlib/tests/script.py`` allows users to write tests in a syntax very close to a shell session,
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using a restricted and limited set of commands that should be enough to mimic
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most of the behaviours.
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A script is a set of commands, each command is composed of:
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* one mandatory command line,
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* one optional set of input lines to feed the command,
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* one optional set of output expected lines,
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* one optional set of error expected lines.
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Input, output and error lines can be specified in any order.
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Except for the expected output, all lines start with a special
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string (based on their origin when used under a Unix shell):
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* '$ ' for the command,
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* nothing for output,
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Comments can be added anywhere, they start with '#' and end with
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The execution stops as soon as an expected output or an expected error is not
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When no output is specified, any ouput from the command is accepted
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and execution continue.
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If an error occurs and no expected error is specified, the execution stops.
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An error is defined by a returned status different from zero, not by the
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presence of text on the error stream.
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The matching is done on a full string comparison basis unless '...' is used, in
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which case expected output/errors can be less precise.
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The following will succeeds only if 'bzr add' outputs 'adding file'::
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If you want the command to succeed for any output, just use::
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The following will stop with an error::
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If you want it to succeed, use::
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2> bzr: ERROR: unknown command "not-a-command"
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You can use ellipsis (...) to replace any piece of text you don't want to be
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$ bzr branch not-a-branch
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2>bzr: ERROR: Not a branch...not-a-branch/".
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This can be used to ignore entire lines too::
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# And here we explain that surprising fourth line
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You can check the content of a file with cat::
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You can also check the existence of a file with cat, the following will fail if
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the file doesn't exist::
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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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ModuleAvailableFeature
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A helper for handling running tests based on whether a python
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module is available. This can handle 3rd-party dependencies (is
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``paramiko`` available?) as well as stdlib (``termios``) or
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extension modules (``bzrlib._groupcompress_pyx``). You create a
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new feature instance with::
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MyModuleFeature = ModuleAvailableFeature('bzrlib.something')
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def test_something(self):
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self.requireFeature(MyModuleFeature)
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something = MyModuleFeature.module
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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
469
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
505
sub-suite of tests in ``test_transport_implementations``. (Most
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per-implementation tests are in submodules of ``bzrlib.tests``, but not
507
the transport tests at the moment.)
509
These tests are repeated for each registered Transport, by generating a
510
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
512
``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.
516
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
519
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
525
a TestProviderAdapter to them, which generates a longer suite containing
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all the test variations.
528
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
540
values to which the test should be applied. The test suite should then
541
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.
550
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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~~~~~~~~~~~~~~~~~~~~~~~~~~~
558
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
563
TestCase in several ways. It adds more assertion methods (e.g.
564
``assertContainsRe``), ``addCleanup``, and other features (see its API
565
docs for details). It also has a ``setUp`` that makes sure that
566
global state like registered hooks and loggers won't interfere with
567
your test. All tests should use this base class (whether directly or
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TestCaseWithMemoryTransport
571
Extends TestCase and adds methods like ``get_transport``,
572
``make_branch`` and ``make_branch_builder``. The files created are
573
stored in a MemoryTransport that is discarded at the end of the test.
574
This class is good for tests that need to make branches or use
575
transports, but that don't require storing things on disk. All tests
576
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
578
real branches in your filesystem.
581
Extends TestCaseWithMemoryTransport. For tests that really do need
582
files to be stored on disk, e.g. because a subprocess uses a file, or
583
for testing functionality that accesses the filesystem directly rather
584
than via the Transport layer (such as dirstate).
586
TestCaseWithTransport
587
Extends TestCaseInTempDir. Provides ``get_url`` and
588
``get_readonly_url`` facilities. Subclasses can control the
589
transports used by setting ``vfs_transport_factory``,
590
``transport_server`` and/or ``transport_readonly_server``.
593
See the API docs for more details.
599
When writing a test for a feature, it is often necessary to set up a
600
branch with a certain history. The ``BranchBuilder`` interface allows the
601
creation of test branches in a quick and easy manner. Here's a sample
604
builder = self.make_branch_builder('relpath')
605
builder.build_commit()
606
builder.build_commit()
607
builder.build_commit()
608
branch = builder.get_branch()
610
``make_branch_builder`` is a method of ``TestCaseWithMemoryTransport``.
612
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
614
give them a ``WorkingTree`` that they can commit to. However, using the
615
newer ``make_branch_builder`` helper is preferred, because it can build
616
the changes in memory, rather than on disk. Tests that are explictly
617
testing how we work with disk objects should, of course, use a real
620
Please see bzrlib.branchbuilder for more details.
622
If you're going to examine the commit timestamps e.g. in a test for log
623
output, you should set the timestamp on the tree, rather than using fuzzy
630
The ``TreeBuilder`` interface allows the construction of arbitrary trees
631
with a declarative interface. A sample session might look like::
633
tree = self.make_branch_and_tree('path')
634
builder = TreeBuilder()
635
builder.start_tree(tree)
636
builder.build(['foo', "bar/", "bar/file"])
637
tree.commit('commit the tree')
638
builder.finish_tree()
640
Usually a test will create a tree using ``make_branch_and_memory_tree`` (a
641
method of ``TestCaseWithMemoryTransport``) or ``make_branch_and_tree`` (a
642
method of ``TestCaseWithTransport``).
644
Please see bzrlib.treebuilder for more details.
647
.. |--| unicode:: U+2014
added
removed
doc/developers/testing.txt
