:mod:`unittest` --- Unit testing framework

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

.. module:: unittest

   :synopsis: Unit testing framework for Python.

.. moduleauthor:: Steve Purcell <stephen_purcell@yahoo.com>

.. sectionauthor:: Steve Purcell <stephen_purcell@yahoo.com>

.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>

.. sectionauthor:: Raymond Hettinger <python@rcn.com>

.. versionadded:: 2.1

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.

:mod:`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 :mod:`unittest` module provides classes that make

it easy to support these qualities for a set of tests.

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

test fixture

   A :dfn:`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 :dfn:`test case` is the smallest unit of testing.  It checks for a specific

   response to a particular set of inputs.  :mod:`unittest` provides a base class,

   :class:`TestCase`, which may be used to create new test cases.

test suite

   A :dfn:`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 :dfn:`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

:class:`TestCase` and :class:`FunctionTestCase` classes; the former should be

used when creating new tests, and the latter can be used when integrating

existing test code with a :mod:`unittest`\ -driven framework. When building test

fixtures using :class:`TestCase`, the :meth:`setUp` and :meth:`tearDown` methods

can be overridden to provide initialization and cleanup for the fixture.  With

:class:`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

:class:`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 :class:`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, :meth:`run`, which

accepts a :class:`TestCase` or :class:`TestSuite` object as a parameter, and

returns a result object.  The class :class:`TestResult` is provided for use as

the result object. :mod:`unittest` provides the :class:`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.

.. seealso::

   Module :mod:`doctest`

      Another test-support module with a very different flavor.

   `Simple Smalltalk Testing: With Patterns <http://www.XProgramming.com/testfram.htm>`_

      Kent Beck's original paper on testing frameworks using the pattern shared by

      :mod:`unittest`.

.. _unittest-minimal-example:

Basic example

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

The :mod:`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 :mod:`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 :class:`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 :meth:`assertEqual` to check for an expected

result; :meth:`assert_` to verify a condition; or :meth:`assertRaises` to verify

that an expected exception gets raised.  These methods are used instead of the

:keyword:`assert` statement so the test runner can accumulate all test results

and produce a report.

When a :meth:`setUp` method is defined, the test runner will run that method

prior to each test.  Likewise, if a :meth:`tearDown` method is defined, the test

runner will invoke that method after each test.  In the example, :meth:`setUp`

was used to create a fresh sequence for each test.

The final block shows a simple way to run the tests. :func:`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 :func:`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 :mod:`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-tests:

Organizing test code

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

The basic building blocks of unit testing are :dfn:`test cases` --- single

scenarios that must be set up and checked for correctness.  In :mod:`unittest`,

test cases are represented by instances of :mod:`unittest`'s :class:`TestCase`

class. To make your own test cases you must write subclasses of

:class:`TestCase`, or use :class:`FunctionTestCase`.

An instance of a :class:`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 :class:`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 :class:`TestCase` subclass will simply override the :meth:`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 :meth:`assert\*` or

:meth:`fail\*` methods provided by the :class:`TestCase` base class.  If the

test fails, an exception will be raised, and :mod:`unittest` will identify the

test case as a :dfn:`failure`.  Any other exceptions will be treated as

:dfn:`errors`. This helps you identify where the problem is: :dfn:`failures` are

caused by incorrect results - a 5 where you expected a 6. :dfn:`Errors` are

caused by incorrect code - e.g., a :exc:`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 :class:`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

:meth:`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 :meth:`setUp` method raises an exception while the test is running, the

framework will consider the test to have suffered an error, and the

:meth:`runTest` method will not be executed.

Similarly, we can provide a :meth:`tearDown` method that tidies up after the

:meth:`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 :meth:`setUp` succeeded, the :meth:`tearDown` method will be run whether

:meth:`runTest` succeeded or not.

Such a working environment for the testing code is called a :dfn:`fixture`.

Often, many small test cases will use the same fixture.  In this case, we would

end up subclassing :class:`SimpleWidgetTestCase` into many small one-method

classes such as :class:`DefaultWidgetSizeTestCase`.  This is time-consuming and

discouraging, so in the same vein as JUnit, :mod:`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 :meth:`runTest` method, but have instead provided

two different test methods.  Class instances will now each run one of the

:meth:`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.

:mod:`unittest` provides a mechanism for this: the :dfn:`test suite`,

represented by :mod:`unittest`'s :class:`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 :class:`TestCase` subclass with many

similarly named test functions, :mod:`unittest` provides a :class:`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``. :class:`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 :func:`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 :class:`TestSuite` instances

can be added to a :class:`TestSuite` just as :class:`TestCase` instances can be

added to a :class:`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 :file:`widget.py`), but there are several

advantages to placing the test code in a separate module, such as

:file:`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.

.. _legacy-unit-tests:

Re-using old test code

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

Some users will find that they have existing test code that they would like to

run from :mod:`unittest`, without converting every old test function to a

:class:`TestCase` subclass.

For this reason, :mod:`unittest` provides a :class:`FunctionTestCase` class.

This subclass of :class:`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, :mod:`unittest` supports tests

raising :exc:`AssertionError` to indicate test failure. However, it is

recommended that you use the explicit :meth:`TestCase.fail\*` and

:meth:`TestCase.assert\*` methods instead, as future versions of :mod:`unittest`

may treat :exc:`AssertionError` differently.

.. note::

   Even though :class:`FunctionTestCase` can be used to quickly convert an existing

   test base over to a :mod:`unittest`\ -based system, this approach is not

   recommended.  Taking the time to set up proper :class:`TestCase` subclasses will

   make future test refactorings infinitely easier.

.. _unittest-contents:

Classes and functions

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

.. class:: TestCase([methodName])

   Instances of the :class:`TestCase` class represent the smallest testable units

   in the :mod:`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 :class:`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 :class:`WidgetTestCase`, each of which runs a

   single test.

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

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

   This class implements the portion of the :class:`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 :mod:`unittest`\

   -based test framework.

.. class:: 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 :class:`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:: TestLoader()

   This class is responsible for loading tests according to various criteria and

   returning them wrapped in a :class:`TestSuite`. It can load all tests within a

   given module or :class:`TestCase` subclass.

.. class:: TestResult()

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

   which have failed.

.. data:: defaultTestLoader

   Instance of the :class:`TestLoader` class intended to be shared.  If no

   customization of the :class:`TestLoader` is needed, this instance can be used

   instead of repeatedly creating new instances.

.. class:: 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.

.. function:: 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 :mod:`doctest`

module.  If so, that module provides a  :class:`DocTestSuite` class that can

automatically build :class:`unittest.TestSuite` instances from the existing

:mod:`doctest`\ -based tests.

.. versionadded:: 2.3

.. _testcase-objects:

TestCase Objects

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

Each :class:`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.

:class:`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:

.. method:: TestCase.setUp()