~bzr-pqm/bzr/bzr.dev : revision 3619.3.1

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Guide to Testing Bazaar

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Testing Bazaar

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##############

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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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contributing today.

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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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failures, like so::

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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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Writing Tests

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=============

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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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- Unit tests

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- Blackbox (UI) tests

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- Per-implementation tests

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- Doctests

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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

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~~~~~~~~~~

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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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quickly.

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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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test.

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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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Blackbox (UI) tests

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~~~~~~~~~~~~~~~~~~~

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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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Doctests

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~~~~~~~~

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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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.. Effort tests

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.. ~~~~~~~~~~~~

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Skipping tests

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--------------

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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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try:

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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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was run and passed.

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Several different cases are distinguished:

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TestSkipped

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Generic skip; the only type that was present up to bzr 0.18.

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TestNotApplicable

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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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at all.

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TestPlatformLimit

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**(Not implemented yet)**

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The test can't be run because of an inherent limitation of the

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environment, such as not having symlinks or not supporting

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unicode.

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UnavailableFeature

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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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KnownFailure

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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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better.

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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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TestPlatformLimit pass pass pass

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TestDependencyMissing 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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For example::

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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. The feature itself

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should provide a ``_probe`` method which is called once to determine if

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it's available.

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These should generally be equivalent to either TestDependencyMissing or

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sometimes TestPlatformLimit.

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Individual tests can also require a feature using the ``requireFeature``

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method::

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self.requireFeature(StraceFeature)

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Features already defined in bzrlib.tests include:

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- SymlinkFeature,

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- HardlinkFeature,

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- OsFifoFeature,

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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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def _probe(self):

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return osutils.has_symlinks()

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def feature_name(self):

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return 'symlinks'

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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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Testing warnings

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----------------

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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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callCatchWarnings.

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The test suite can be run with ``-Werror`` to check no unexpected errors

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occur.

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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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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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classes.

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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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Test scenarios

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--------------

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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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Test support

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------------

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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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write your tests.

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TestCase

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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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via a subclass).

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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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TestCaseInTempDir

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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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BranchBuilder

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~~~~~~~~~~~~~

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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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session::

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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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``WorkingTree``.

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Please see bzrlib.branchbuilder for more details.

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TreeBuilder

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~~~~~~~~~~~

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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

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..

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vim: ft=rst tw=74 ai