
``unittest`` --- Unit testing framework
***************************************

The Python unit testing framework, sometimes referred to as "PyUnit,"
is a Python language version of JUnit, by Kent Beck and Erich Gamma.
JUnit is, in turn, a Java version of Kent's Smalltalk testing
framework.  Each is the de facto standard unit testing framework for
its respective language.

``unittest`` supports test automation, sharing of setup and shutdown
code for tests, aggregation of tests into collections, and
independence of the tests from the reporting framework.  The
``unittest`` module provides classes that make it easy to support
these qualities for a set of tests.

To achieve this, ``unittest`` supports some important concepts:

test fixture
   A *test fixture* represents the preparation needed to perform one
   or more tests, and any associate cleanup actions.  This may
   involve, for example, creating temporary or proxy databases,
   directories, or starting a server process.

test case
   A *test case* is the smallest unit of testing.  It checks for a
   specific response to a particular set of inputs.  ``unittest``
   provides a base class, ``TestCase``, which may be used to create
   new test cases.

test suite
   A *test suite* is a collection of test cases, test suites, or both.
   It is used to aggregate tests that should be executed together.

test runner
   A *test runner* is a component which orchestrates the execution of
   tests and provides the outcome to the user.  The runner may use a
   graphical interface, a textual interface, or return a special value
   to indicate the results of executing the tests.

The test case and test fixture concepts are supported through the
``TestCase`` and ``FunctionTestCase`` classes; the former should be
used when creating new tests, and the latter can be used when
integrating existing test code with a ``unittest``-driven framework.
When building test fixtures using ``TestCase``, the ``setUp()`` and
``tearDown()`` methods can be overridden to provide initialization and
cleanup for the fixture.  With ``FunctionTestCase``, existing
functions can be passed to the constructor for these purposes.  When
the test is run, the fixture initialization is run first; if it
succeeds, the cleanup method is run after the test has been executed,
regardless of the outcome of the test.  Each instance of the
``TestCase`` will only be used to run a single test method, so a new
fixture is created for each test.

Test suites are implemented by the ``TestSuite`` class.  This class
allows individual tests and test suites to be aggregated; when the
suite is executed, all tests added directly to the suite and in
"child" test suites are run.

A test runner is an object that provides a single method, ``run()``,
which accepts a ``TestCase`` or ``TestSuite`` object as a parameter,
and returns a result object.  The class ``TestResult`` is provided for
use as the result object. ``unittest`` provides the ``TextTestRunner``
as an example test runner which reports test results on the standard
error stream by default.  Alternate runners can be implemented for
other environments (such as graphical environments) without any need
to derive from a specific class.

See also:

   Module ``doctest``
      Another test-support module with a very different flavor.

   Simple Smalltalk Testing: With Patterns
      Kent Beck's original paper on testing frameworks using the
      pattern shared by ``unittest``.


Basic example
=============

The ``unittest`` module provides a rich set of tools for constructing
and running tests.  This section demonstrates that a small subset of
the tools suffice to meet the needs of most users.

Here is a short script to test three functions from the ``random``
module:

   import random
   import unittest

   class TestSequenceFunctions(unittest.TestCase):

       def setUp(self):
           self.seq = range(10)

       def testshuffle(self):
           # make sure the shuffled sequence does not lose any elements
           random.shuffle(self.seq)
           self.seq.sort()
           self.assertEqual(self.seq, range(10))

       def testchoice(self):
           element = random.choice(self.seq)
           self.assert_(element in self.seq)

       def testsample(self):
           self.assertRaises(ValueError, random.sample, self.seq, 20)
           for element in random.sample(self.seq, 5):
               self.assert_(element in self.seq)

   if __name__ == '__main__':
       unittest.main()

A testcase is created by subclassing ``unittest.TestCase``. The three
individual tests are defined with methods whose names start with the
letters ``test``.  This naming convention informs the test runner
about which methods represent tests.

The crux of each test is a call to ``assertEqual()`` to check for an
expected result; ``assert_()`` to verify a condition; or
``assertRaises()`` to verify that an expected exception gets raised.
These methods are used instead of the ``assert`` statement so the test
runner can accumulate all test results and produce a report.

When a ``setUp()`` method is defined, the test runner will run that
method prior to each test.  Likewise, if a ``tearDown()`` method is
defined, the test runner will invoke that method after each test.  In
the example, ``setUp()`` was used to create a fresh sequence for each
test.

The final block shows a simple way to run the tests.
``unittest.main()`` provides a command line interface to the test
script.  When run from the command line, the above script produces an
output that looks like this:

   ...
   ----------------------------------------------------------------------
   Ran 3 tests in 0.000s

   OK

Instead of ``unittest.main()``, there are other ways to run the tests
with a finer level of control, less terse output, and no requirement
to be run from the command line.  For example, the last two lines may
be replaced with:

   suite = unittest.TestLoader().loadTestsFromTestCase(TestSequenceFunctions)
   unittest.TextTestRunner(verbosity=2).run(suite)

Running the revised script from the interpreter or another script
produces the following output:

   testchoice (__main__.TestSequenceFunctions) ... ok
   testsample (__main__.TestSequenceFunctions) ... ok
   testshuffle (__main__.TestSequenceFunctions) ... ok

   ----------------------------------------------------------------------
   Ran 3 tests in 0.110s

   OK

The above examples show the most commonly used ``unittest`` features
which are sufficient to meet many everyday testing needs.  The
remainder of the documentation explores the full feature set from
first principles.


Organizing test code
====================

The basic building blocks of unit testing are *test cases* --- single
scenarios that must be set up and checked for correctness.  In
``unittest``, test cases are represented by instances of
``unittest``'s ``TestCase`` class. To make your own test cases you
must write subclasses of ``TestCase``, or use ``FunctionTestCase``.

An instance of a ``TestCase``-derived class is an object that can
completely run a single test method, together with optional set-up and
tidy-up code.

The testing code of a ``TestCase`` instance should be entirely self
contained, such that it can be run either in isolation or in arbitrary
combination with any number of other test cases.

The simplest ``TestCase`` subclass will simply override the
``runTest()`` method in order to perform specific testing code:

   import unittest

   class DefaultWidgetSizeTestCase(unittest.TestCase):
       def runTest(self):
           widget = Widget('The widget')
           self.assertEqual(widget.size(), (50, 50), 'incorrect default size')

Note that in order to test something, we use the one of the
``assert*()`` or ``fail*()`` methods provided by the ``TestCase`` base
class.  If the test fails, an exception will be raised, and
``unittest`` will identify the test case as a *failure*.  Any other
exceptions will be treated as *errors*. This helps you identify where
the problem is: *failures* are caused by incorrect results - a 5 where
you expected a 6. *Errors* are caused by incorrect code - e.g., a
``TypeError`` caused by an incorrect function call.

The way to run a test case will be described later.  For now, note
that to construct an instance of such a test case, we call its
constructor without arguments:

   testCase = DefaultWidgetSizeTestCase()

Now, such test cases can be numerous, and their set-up can be
repetitive.  In the above case, constructing a ``Widget`` in each of
100 Widget test case subclasses would mean unsightly duplication.

Luckily, we can factor out such set-up code by implementing a method
called ``setUp()``, which the testing framework will automatically
call for us when we run the test:

   import unittest

   class SimpleWidgetTestCase(unittest.TestCase):
       def setUp(self):
           self.widget = Widget('The widget')

   class DefaultWidgetSizeTestCase(SimpleWidgetTestCase):
       def runTest(self):
           self.failUnless(self.widget.size() == (50,50),
                           'incorrect default size')

   class WidgetResizeTestCase(SimpleWidgetTestCase):
       def runTest(self):
           self.widget.resize(100,150)
           self.failUnless(self.widget.size() == (100,150),
                           'wrong size after resize')

If the ``setUp()`` method raises an exception while the test is
running, the framework will consider the test to have suffered an
error, and the ``runTest()`` method will not be executed.

Similarly, we can provide a ``tearDown()`` method that tidies up after
the ``runTest()`` method has been run:

   import unittest

   class SimpleWidgetTestCase(unittest.TestCase):
       def setUp(self):
           self.widget = Widget('The widget')

       def tearDown(self):
           self.widget.dispose()
           self.widget = None

If ``setUp()`` succeeded, the ``tearDown()`` method will be run
whether ``runTest()`` succeeded or not.

Such a working environment for the testing code is called a *fixture*.

Often, many small test cases will use the same fixture.  In this case,
we would end up subclassing ``SimpleWidgetTestCase`` into many small
one-method classes such as ``DefaultWidgetSizeTestCase``.  This is
time-consuming and discouraging, so in the same vein as JUnit,
``unittest`` provides a simpler mechanism:

   import unittest

   class WidgetTestCase(unittest.TestCase):
       def setUp(self):
           self.widget = Widget('The widget')

       def tearDown(self):
           self.widget.dispose()
           self.widget = None

       def testDefaultSize(self):
           self.failUnless(self.widget.size() == (50,50),
                           'incorrect default size')

       def testResize(self):
           self.widget.resize(100,150)
           self.failUnless(self.widget.size() == (100,150),
                           'wrong size after resize')

Here we have not provided a ``runTest()`` method, but have instead
provided two different test methods.  Class instances will now each
run one of the ``test*()``  methods, with ``self.widget`` created and
destroyed separately for each instance.  When creating an instance we
must specify the test method it is to run.  We do this by passing the
method name in the constructor:

   defaultSizeTestCase = WidgetTestCase('testDefaultSize')
   resizeTestCase = WidgetTestCase('testResize')

Test case instances are grouped together according to the features
they test. ``unittest`` provides a mechanism for this: the *test
suite*, represented by ``unittest``'s ``TestSuite`` class:

   widgetTestSuite = unittest.TestSuite()
   widgetTestSuite.addTest(WidgetTestCase('testDefaultSize'))
   widgetTestSuite.addTest(WidgetTestCase('testResize'))

For the ease of running tests, as we will see later, it is a good idea
to provide in each test module a callable object that returns a pre-
built test suite:

   def suite():
       suite = unittest.TestSuite()
       suite.addTest(WidgetTestCase('testDefaultSize'))
       suite.addTest(WidgetTestCase('testResize'))
       return suite

or even:

   def suite():
       tests = ['testDefaultSize', 'testResize']

       return unittest.TestSuite(map(WidgetTestCase, tests))

Since it is a common pattern to create a ``TestCase`` subclass with
many similarly named test functions, ``unittest`` provides a
``TestLoader`` class that can be used to automate the process of
creating a test suite and populating it with individual tests. For
example,

   suite = unittest.TestLoader().loadTestsFromTestCase(WidgetTestCase)

will create a test suite that will run
``WidgetTestCase.testDefaultSize()`` and
``WidgetTestCase.testResize``. ``TestLoader`` uses the ``'test'``
method name prefix to identify test methods automatically.

Note that the order in which the various test cases will be run is
determined by sorting the test function names with the built-in
``cmp()`` function.

Often it is desirable to group suites of test cases together, so as to
run tests for the whole system at once.  This is easy, since
``TestSuite`` instances can be added to a ``TestSuite`` just as
``TestCase`` instances can be added to a ``TestSuite``:

   suite1 = module1.TheTestSuite()
   suite2 = module2.TheTestSuite()
   alltests = unittest.TestSuite([suite1, suite2])

You can place the definitions of test cases and test suites in the
same modules as the code they are to test (such as ``widget.py``), but
there are several advantages to placing the test code in a separate
module, such as ``test_widget.py``:

* The test module can be run standalone from the command line.

* The test code can more easily be separated from shipped code.

* There is less temptation to change test code to fit the code it
  tests without a good reason.

* Test code should be modified much less frequently than the code it
  tests.

* Tested code can be refactored more easily.

* Tests for modules written in C must be in separate modules anyway,
  so why not be consistent?

* If the testing strategy changes, there is no need to change the
  source code.


Re-using old test code
======================

Some users will find that they have existing test code that they would
like to run from ``unittest``, without converting every old test
function to a ``TestCase`` subclass.

For this reason, ``unittest`` provides a ``FunctionTestCase`` class.
This subclass of ``TestCase`` can be used to wrap an existing test
function.  Set-up and tear-down functions can also be provided.

Given the following test function:

   def testSomething():
       something = makeSomething()
       assert something.name is not None
       # ...

one can create an equivalent test case instance as follows:

   testcase = unittest.FunctionTestCase(testSomething)

If there are additional set-up and tear-down methods that should be
called as part of the test case's operation, they can also be provided
like so:

   testcase = unittest.FunctionTestCase(testSomething,
                                        setUp=makeSomethingDB,
                                        tearDown=deleteSomethingDB)

To make migrating existing test suites easier, ``unittest`` supports
tests raising ``AssertionError`` to indicate test failure. However, it
is recommended that you use the explicit ``TestCase.fail*()`` and
``TestCase.assert*()`` methods instead, as future versions of
``unittest`` may treat ``AssertionError`` differently.

Note: Even though ``FunctionTestCase`` can be used to quickly convert an
  existing test base over to a ``unittest``-based system, this
  approach is not recommended.  Taking the time to set up proper
  ``TestCase`` subclasses will make future test refactorings
  infinitely easier.


Classes and functions
=====================

class unittest.TestCase([methodName])

   Instances of the ``TestCase`` class represent the smallest testable
   units in the ``unittest`` universe.  This class is intended to be
   used as a base class, with specific tests being implemented by
   concrete subclasses.  This class implements the interface needed by
   the test runner to allow it to drive the test, and methods that the
   test code can use to check for and report various kinds of failure.

   Each instance of ``TestCase`` will run a single test method: the
   method named *methodName*.  If you remember, we had an earlier
   example that went something like this:

      def suite():
          suite = unittest.TestSuite()
          suite.addTest(WidgetTestCase('testDefaultSize'))
          suite.addTest(WidgetTestCase('testResize'))
          return suite

   Here, we create two instances of ``WidgetTestCase``, each of which
   runs a single test.

   *methodName* defaults to ``'runTest'``.

class unittest.FunctionTestCase(testFunc[, setUp[, tearDown[, description]]])

   This class implements the portion of the ``TestCase`` interface
   which allows the test runner to drive the test, but does not
   provide the methods which test code can use to check and report
   errors. This is used to create test cases using legacy test code,
   allowing it to be integrated into a ``unittest``-based test
   framework.

class unittest.TestSuite([tests])

   This class represents an aggregation of individual tests cases and
   test suites. The class presents the interface needed by the test
   runner to allow it to be run as any other test case.  Running a
   ``TestSuite`` instance is the same as iterating over the suite,
   running each test individually.

   If *tests* is given, it must be an iterable of individual test
   cases or other test suites that will be used to build the suite
   initially. Additional methods are provided to add test cases and
   suites to the collection later on.

class unittest.TestLoader

   This class is responsible for loading tests according to various
   criteria and returning them wrapped in a ``TestSuite``. It can load
   all tests within a given module or ``TestCase`` subclass.

class unittest.TestResult

   This class is used to compile information about which tests have
   succeeded and which have failed.

unittest.defaultTestLoader

   Instance of the ``TestLoader`` class intended to be shared.  If no
   customization of the ``TestLoader`` is needed, this instance can be
   used instead of repeatedly creating new instances.

class unittest.TextTestRunner([stream[, descriptions[, verbosity]]])

   A basic test runner implementation which prints results on standard
   error.  It has a few configurable parameters, but is essentially
   very simple.  Graphical applications which run test suites should
   provide alternate implementations.

unittest.main([module[, defaultTest[, argv[, testRunner[, testLoader]]]]])

   A command-line program that runs a set of tests; this is primarily
   for making test modules conveniently executable.  The simplest use
   for this function is to include the following line at the end of a
   test script:

      if __name__ == '__main__':
          unittest.main()

   The *testRunner* argument can either be a test runner class or an
   already created instance of it.

In some cases, the existing tests may have been written using the
``doctest`` module.  If so, that module provides a  ``DocTestSuite``
class that can automatically build ``unittest.TestSuite`` instances
from the existing ``doctest``-based tests.


TestCase Objects
================

Each ``TestCase`` instance represents a single test, but each concrete
subclass may be used to define multiple tests --- the concrete class
represents a single test fixture.  The fixture is created and cleaned
up for each test case.

``TestCase`` instances provide three groups of methods: one group used
to run the test, another used by the test implementation to check
conditions and report failures, and some inquiry methods allowing
information about the test itself to be gathered.

Methods in the first group (running the test) are:

TestCase.setUp()

   Method called to prepare the test fixture.  This is called
   immediately before calling the test method; any exception raised by
   this method will be considered an error rather than a test failure.
   The default implementation does nothing.

TestCase.tearDown()

   Method called immediately after the test method has been called and
   the result recorded.  This is called even if the test method raised
   an exception, so the implementation in subclasses may need to be
   particularly careful about checking internal state.  Any exception
   raised by this method will be considered an error rather than a
   test failure.  This method will only be called if the ``setUp()``
   succeeds, regardless of the outcome of the test method. The default
   implementation does nothing.

TestCase.run([result])

   Run the test, collecting the result into the test result object
   passed as *result*.  If *result* is omitted or ``None``, a
   temporary result object is created (by calling the
   ``defaultTestCase()`` method) and used; this result object is not
   returned to ``run()``'s caller.

   The same effect may be had by simply calling the ``TestCase``
   instance.

TestCase.debug()

   Run the test without collecting the result.  This allows exceptions
   raised by the test to be propagated to the caller, and can be used
   to support running tests under a debugger.

The test code can use any of the following methods to check for and
report failures.

TestCase.assert_(expr[, msg])
TestCase.failUnless(expr[, msg])
TestCase.assertTrue(expr[, msg])

   Signal a test failure if *expr* is false; the explanation for the
   error will be *msg* if given, otherwise it will be ``None``.

TestCase.assertEqual(first, second[, msg])
TestCase.failUnlessEqual(first, second[, msg])

   Test that *first* and *second* are equal.  If the values do not
   compare equal, the test will fail with the explanation given by
   *msg*, or ``None``.  Note that using ``failUnlessEqual()`` improves
   upon doing the comparison as the first parameter to
   ``failUnless()``:  the default value for *msg* can be computed to
   include representations of both *first* and *second*.

TestCase.assertNotEqual(first, second[, msg])
TestCase.failIfEqual(first, second[, msg])

   Test that *first* and *second* are not equal.  If the values do
   compare equal, the test will fail with the explanation given by
   *msg*, or ``None``.  Note that using ``failIfEqual()`` improves
   upon doing the comparison as the first parameter to
   ``failUnless()`` is that the default value for *msg* can be
   computed to include representations of both *first* and *second*.

TestCase.assertAlmostEqual(first, second[, places[, msg]])
TestCase.failUnlessAlmostEqual(first, second[, places[, msg]])

   Test that *first* and *second* are approximately equal by computing
   the difference, rounding to the given number of decimal *places*
   (default 7), and comparing to zero. Note that comparing a given
   number of decimal places is not the same as comparing a given
   number of significant digits. If the values do not compare equal,
   the test will fail with the explanation given by *msg*, or
   ``None``.

TestCase.assertNotAlmostEqual(first, second[, places[, msg]])
TestCase.failIfAlmostEqual(first, second[, places[, msg]])

   Test that *first* and *second* are not approximately equal by
   computing the difference, rounding to the given number of decimal
   *places* (default 7), and comparing to zero. Note that comparing a
   given number of decimal places is not the same as comparing a given
   number of significant digits. If the values do not compare equal,
   the test will fail with the explanation given by *msg*, or
   ``None``.

TestCase.assertRaises(exception, callable, ...)
TestCase.failUnlessRaises(exception, callable, ...)

   Test that an exception is raised when *callable* is called with any
   positional or keyword arguments that are also passed to
   ``assertRaises()``.  The test passes if *exception* is raised, is
   an error if another exception is raised, or fails if no exception
   is raised.  To catch any of a group of exceptions, a tuple
   containing the exception classes may be passed as *exception*.

TestCase.failIf(expr[, msg])
TestCase.assertFalse(expr[, msg])

   The inverse of the ``failUnless()`` method is the ``failIf()``
   method.  This signals a test failure if *expr* is true, with *msg*
   or ``None`` for the error message.

TestCase.fail([msg])

   Signals a test failure unconditionally, with *msg* or ``None`` for
   the error message.

TestCase.failureException

   This class attribute gives the exception raised by the ``test()``
   method.  If a test framework needs to use a specialized exception,
   possibly to carry additional information, it must subclass this
   exception in order to "play fair" with the framework.  The initial
   value of this attribute is ``AssertionError``.

Testing frameworks can use the following methods to collect
information on the test:

TestCase.countTestCases()

   Return the number of tests represented by this test object.  For
   ``TestCase`` instances, this will always be ``1``.

TestCase.defaultTestResult()

   Return an instance of the test result class that should be used for
   this test case class (if no other result instance is provided to
   the ``run()`` method).

   For ``TestCase`` instances, this will always be an instance of
   ``TestResult``;  subclasses of ``TestCase`` should override this as
   necessary.

TestCase.id()

   Return a string identifying the specific test case.  This is
   usually the full name of the test method, including the module and
   class name.

TestCase.shortDescription()

   Returns a one-line description of the test, or ``None`` if no
   description has been provided.  The default implementation of this
   method returns the first line of the test method's docstring, if
   available, or ``None``.


TestSuite Objects
=================

``TestSuite`` objects behave much like ``TestCase`` objects, except
they do not actually implement a test.  Instead, they are used to
aggregate tests into groups of tests that should be run together. Some
additional methods are available to add tests to ``TestSuite``
instances:

TestSuite.addTest(test)

   Add a ``TestCase`` or ``TestSuite`` to the suite.

TestSuite.addTests(tests)

   Add all the tests from an iterable of ``TestCase`` and
   ``TestSuite`` instances to this test suite.

   This is equivalent to iterating over *tests*, calling ``addTest()``
   for each element.

``TestSuite`` shares the following methods with ``TestCase``:

TestSuite.run(result)

   Run the tests associated with this suite, collecting the result
   into the test result object passed as *result*.  Note that unlike
   ``TestCase.run()``, ``TestSuite.run()`` requires the result object
   to be passed in.

TestSuite.debug()

   Run the tests associated with this suite without collecting the
   result. This allows exceptions raised by the test to be propagated
   to the caller and can be used to support running tests under a
   debugger.

TestSuite.countTestCases()

   Return the number of tests represented by this test object,
   including all individual tests and sub-suites.

In the typical usage of a ``TestSuite`` object, the ``run()`` method
is invoked by a ``TestRunner`` rather than by the end-user test
harness.


TestResult Objects
==================

A ``TestResult`` object stores the results of a set of tests.  The
``TestCase`` and ``TestSuite`` classes ensure that results are
properly recorded; test authors do not need to worry about recording
the outcome of tests.

Testing frameworks built on top of ``unittest`` may want access to the
``TestResult`` object generated by running a set of tests for
reporting purposes; a ``TestResult`` instance is returned by the
``TestRunner.run()`` method for this purpose.

``TestResult`` instances have the following attributes that will be of
interest when inspecting the results of running a set of tests:

TestResult.errors

   A list containing 2-tuples of ``TestCase`` instances and strings
   holding formatted tracebacks. Each tuple represents a test which
   raised an unexpected exception.

TestResult.failures

   A list containing 2-tuples of ``TestCase`` instances and strings
   holding formatted tracebacks. Each tuple represents a test where a
   failure was explicitly signalled using the ``TestCase.fail*()`` or
   ``TestCase.assert*()`` methods.

TestResult.testsRun

   The total number of tests run so far.

TestResult.wasSuccessful()

   Returns ``True`` if all tests run so far have passed, otherwise
   returns ``False``.

TestResult.stop()

   This method can be called to signal that the set of tests being run
   should be aborted by setting the ``TestResult``'s ``shouldStop``
   attribute to ``True``.  ``TestRunner`` objects should respect this
   flag and return without running any additional tests.

   For example, this feature is used by the ``TextTestRunner`` class
   to stop the test framework when the user signals an interrupt from
   the keyboard. Interactive tools which provide ``TestRunner``
   implementations can use this in a similar manner.

The following methods of the ``TestResult`` class are used to maintain
the internal data structures, and may be extended in subclasses to
support additional reporting requirements.  This is particularly
useful in building tools which support interactive reporting while
tests are being run.

TestResult.startTest(test)

   Called when the test case *test* is about to be run.

   The default implementation simply increments the instance's
   ``testsRun`` counter.

TestResult.stopTest(test)

   Called after the test case *test* has been executed, regardless of
   the outcome.

   The default implementation does nothing.

TestResult.addError(test, err)

   Called when the test case *test* raises an unexpected exception
   *err* is a tuple of the form returned by ``sys.exc_info()``:
   ``(type, value, traceback)``.

   The default implementation appends a tuple ``(test,
   formatted_err)`` to the instance's ``errors`` attribute, where
   *formatted_err* is a formatted traceback derived from *err*.

TestResult.addFailure(test, err)

   Called when the test case *test* signals a failure. *err* is a
   tuple of the form returned by ``sys.exc_info()``:  ``(type, value,
   traceback)``.

   The default implementation appends a tuple ``(test,
   formatted_err)`` to the instance's ``failures`` attribute, where
   *formatted_err* is a formatted traceback derived from *err*.

TestResult.addSuccess(test)

   Called when the test case *test* succeeds.

   The default implementation does nothing.


TestLoader Objects
==================

The ``TestLoader`` class is used to create test suites from classes
and modules.  Normally, there is no need to create an instance of this
class; the ``unittest`` module provides an instance that can be shared
as ``unittest.defaultTestLoader``. Using a subclass or instance,
however, allows customization of some configurable properties.

``TestLoader`` objects have the following methods:

TestLoader.loadTestsFromTestCase(testCaseClass)

   Return a suite of all tests cases contained in the
   ``TestCase``-derived ``testCaseClass``.

TestLoader.loadTestsFromModule(module)

   Return a suite of all tests cases contained in the given module.
   This method searches *module* for classes derived from ``TestCase``
   and creates an instance of the class for each test method defined
   for the class.

   Warning: While using a hierarchy of ``TestCase``-derived classes can be
     convenient in sharing fixtures and helper functions, defining
     test methods on base classes that are not intended to be
     instantiated directly does not play well with this method.  Doing
     so, however, can be useful when the fixtures are different and
     defined in subclasses.

TestLoader.loadTestsFromName(name[, module])

   Return a suite of all tests cases given a string specifier.

   The specifier *name* is a "dotted name" that may resolve either to
   a module, a test case class, a test method within a test case
   class, a ``TestSuite`` instance, or a callable object which returns
   a ``TestCase`` or ``TestSuite`` instance.  These checks are applied
   in the order listed here; that is, a method on a possible test case
   class will be picked up as "a test method within a test case
   class", rather than "a callable object".

   For example, if you have a module ``SampleTests`` containing a
   ``TestCase``-derived class ``SampleTestCase`` with three test
   methods (``test_one()``, ``test_two()``, and ``test_three()``), the
   specifier ``'SampleTests.SampleTestCase'`` would cause this method
   to return a suite which will run all three test methods.  Using the
   specifier ``'SampleTests.SampleTestCase.test_two'`` would cause it
   to return a test suite which will run only the ``test_two()`` test
   method.  The specifier can refer to modules and packages which have
   not been imported; they will be imported as a side-effect.

   The method optionally resolves *name* relative to the given
   *module*.

TestLoader.loadTestsFromNames(names[, module])

   Similar to ``loadTestsFromName()``, but takes a sequence of names
   rather than a single name.  The return value is a test suite which
   supports all the tests defined for each name.

TestLoader.getTestCaseNames(testCaseClass)

   Return a sorted sequence of method names found within
   *testCaseClass*; this should be a subclass of ``TestCase``.

The following attributes of a ``TestLoader`` can be configured either
by subclassing or assignment on an instance:

TestLoader.testMethodPrefix

   String giving the prefix of method names which will be interpreted
   as test methods.  The default value is ``'test'``.

   This affects ``getTestCaseNames()`` and all the
   ``loadTestsFrom*()`` methods.

TestLoader.sortTestMethodsUsing

   Function to be used to compare method names when sorting them in
   ``getTestCaseNames()`` and all the ``loadTestsFrom*()`` methods.
   The default value is the built-in ``cmp()`` function; the attribute
   can also be set to ``None`` to disable the sort.

TestLoader.suiteClass

   Callable object that constructs a test suite from a list of tests.
   No methods on the resulting object are needed.  The default value
   is the ``TestSuite`` class.

   This affects all the ``loadTestsFrom*()`` methods.
