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# 25.3. `unittest` — Unit testing framework

Changed in version 3.1: Added test skipping and expected failures.

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`.
Nose and py.test
  Third-party unittest frameworks with a lighter-weight syntax for writing tests. For example, `assert func(10) == 42`.
python-mock and minimock
  Tools for creating mock test objects (objects simulating external resources).

## 25.3.1. 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 test_shuffle(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 test_choice(self):
            element = random.choice(self.seq)
            self.assert_(element in self.seq)

        def test_sample(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.

## 25.3.2. 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*()` 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.assertTrue(self.widget.size() == (50,50),
                            'incorrect default size')

    class WidgetResizeTestCase(SimpleWidgetTestCase):
        def runTest(self):
            self.widget.resize(100,150)
            self.assertTrue(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.assertTrue(self.widget.size() == (50,50),
                            'incorrect default size')

        def testResize(self):
            self.widget.resize(100,150)
            self.assertTrue(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 respect to the built-in ordering for strings.

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.

## 25.3.3. 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.

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

## 25.3.4. Skipping tests and expected failures

Unittest supports skipping individual test methods and even whole classes of tests. In addition, it supports marking a test as a “expected failure,” a test that is broken and will fail, but shouldn’t be counted as a failure on a `TestResult`.

Skipping a test is simply a matter of using the `skip()` decorator or one of its conditional variants.

Basic skipping looks like this:

    class MyTestCase(unittest.TestCase):

        @unittest.skip("demonstrating skipping")
        def test_nothing(self):
            self.fail("shouldn't happen")

        @unittest.skipIf(mylib.__version__ < (1, 3), "not supported in this library version")
        def test_format(self):
            # Tests that work for only a certain version of the library.
            pass

        @unittest.skipUnless(sys.platform.startswith("win"), "requires Windows")
        def test_windows_support(self):
            # windows specific testing code
            pass

This is the output of running the example above in verbose mode:

    test_format (__main__.MyTestCase) ... skipped 'not supported in this library version'
    test_nothing (__main__.MyTestCase) ... skipped 'demonstrating skipping'
    test_windows_support (__main__.MyTestCase) ... skipped 'requires Windows'

    ----------------------------------------------------------------------
    Ran 3 tests in 0.005s

    OK (skipped=3)

Classes can be skipped just like methods:

    @skip("showing class skipping")
    class MySkippedTestCase(unittest.TestCase):
        def test_not_run(self):
            pass

`TestCase.setUp()` can also skip the test. This is useful when a resource that needs to be set up is not available.

Expected failures use the `expectedFailure()` decorator.

    class ExpectedFailureTestCase(unittest.TestCase):
        @unittest.expectedFailure
        def test_fail(self):
            self.assertEqual(1, 0, "broken")

It’s easy to roll your own skipping decorators by making a decorator that calls `skip()` on the test when it wants it to be skipped. This decorator skips the test unless the passed object has a certain attribute:

    def skipUnlessHasattr(obj, attr):
        if hasattr(obj, attr):
            return lambda func: func
        return unittest.skip("{0!r} doesn't have {1!r}".format(obj, attr))

The following decorators implement test skipping and expected failures:

`unittest.``skip`(reason)
  Unconditionally skip the decorated test. reason should describe why the test is being skipped.

`unittest.``skipIf`(condition, reason)
  Skip the decorated test if condition is true.

`unittest.``skipUnless`(condition, reason)
  Skip the decoratored test unless condition is true.

`unittest.``expectedFailure`()
  Mark the test as an expected failure. If the test fails when run, the test is not counted as a failure.

## 25.3.5. Classes and functions

This section describes in depth the API of `unittest`.

### 25.3.5.1. Test cases

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()`.

  `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:

  `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.
  `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.
  `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.

  `skipTest`(reason)
    Calling this during the a test method or `setUp()` skips the current test. See Skipping tests and expected failures for more information.
  `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.

  `assertTrue`(expr[, msg])
  `assert_`(expr[, msg])
  `failUnless`(expr[, msg])

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

    Deprecated since version 3.1: `failUnless()`.

  `assertEqual`(first, second[, msg])
  `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 `assertEqual()` improves upon doing the comparison as the first parameter to `assertTrue()`: the default value for msg include representations of both first and second.

    In addition, if first and second are the exact same type and one of list, tuple, dict, set, or frozenset or any type that a subclass registers `addTypeEqualityFunc()` the type specific equality function will be called in order to generate a more useful default error message.

    Changed in version 3.1: Added the automatic calling of type specific equality function.

    Deprecated since version 3.1: `failUnlessEqual()`.

  `assertNotEqual`(first, second[, msg])
  `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 `assertNotEqual()` improves upon doing the comparison as the first parameter to `assertTrue()` is that the default value for msg can be computed to include representations of both first and second.

    Deprecated since version 3.1: `failIfEqual()`.

  `assertAlmostEqual`(first, second[, places[, msg]])
  `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`.

    Deprecated since version 3.1: `failUnlessAlmostEqual()`.

  `assertNotAlmostEqual`(first, second[, places[, msg]])
  `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`.

    Deprecated since version 3.1: `failIfAlmostEqual()`.

  `assertGreater`(first, second, msg=None)
  `assertGreaterEqual`(first, second, msg=None)
  `assertLess`(first, second, msg=None)
  `assertLessEqual`(first, second, msg=None)

    Test that first is respectively >, >=, < or <= than second depending on the method name. If not, the test will fail with an explanation or with the explanation given by msg:

        >>> self.assertGreaterEqual(3, 4)
        AssertionError: "3" unexpectedly not greater than or equal to "4"

    New in version 3.1.

  `assertMultiLineEqual`(self, first, second, msg=None)

    Test that the multiline string first is equal to the string second. When not equal a diff of the two strings highlighting the differences will be included in the error message.

    If specified msg will be used as the error message on failure.

    New in version 3.1.

  `assertRegexpMatches(text, regexp[, msg=None]):`

    Verifies that a regexp search matches text. Fails with an error message including the pattern and the text. regexp may be a regular expression object or a string containing a regular expression suitable for use by `re.search()`.

    New in version 3.1.

  `assertIn`(first, second, msg=None)
  `assertNotIn`(first, second, msg=None)

    Tests that first is or is not in second with an explanatory error message as appropriate.

    If specified msg will be used as the error message on failure.

    New in version 3.1.

  `assertSameElements`(expected, actual, msg=None)

    Test that sequence expected contains the same elements as actual. When they don’t an error message listing the differences between the sequences will be generated.

    If specified msg will be used as the error message on failure.

    New in version 3.1.

  `assertSetEqual`(set1, set2, msg=None)

    Tests that two sets are equal. If not, an error message is constructed that lists the differences between the sets.

    Fails if either of set1 or set2 does not have a `set.difference()` method.

    If specified msg will be used as the error message on failure.

    New in version 3.1.

  `assertDictEqual`(expected, actual, msg=None)

    Test that two dictionaries are equal. If not, an error message is constructed that shows the differences in the dictionaries.

    If specified msg will be used as the error message on failure.

    New in version 3.1.

  `assertDictContainsSubset`(expected, actual, msg=None)

    Tests whether the key/value pairs in dictionary actual are a superset of those in expected. If not, an error message listing the missing keys and mismatched values is generated.

    If specified msg will be used as the error message on failure.

    New in version 3.1.

  `assertListEqual`(list1, list2, msg=None)
  `assertTupleEqual`(tuple1, tuple2, msg=None)

    Tests that two lists or tuples are equal. If not an error message is constructed that shows only the differences between the two. An error is also raised if either of the parameters are of the wrong type.

    If specified msg will be used as the error message on failure.

    New in version 3.1.

  `assertSequenceEqual`(seq1, seq2, msg=None, seq_type=None)

    Tests that two sequences are equal. If a seq_type is supplied, both seq1 and seq2 must be instances of seq_type or a failure will be raised. If the sequences are different an error message is constructed that shows the difference between the two.

    If specified msg will be used as the error message on failure.

    This method is used to implement `assertListEqual()` and `assertTupleEqual()`.

    New in version 3.1.

  `assertRaises`(exception[, callable, ...])
  `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.

    If callable is omitted or None, returns a context manager so that the code under test can be written inline rather than as a function:

        with self.failUnlessRaises(some_error_class):
            do_something()

    Changed in version 3.1: Added the ability to use `assertRaises()` as a context manager.

    Deprecated since version 3.1: `failUnlessRaises()`.

  `assertRaisesRegexp`(exception, regexp[, callable, ...])

    Like `assertRaises()` but also tests that regexp matches on the string representation of the raised exception. regexp may be a regular expression object or a string containing a regular expression suitable for use by `re.search()`. Examples:

        self.assertRaisesRegexp(ValueError, 'invalid literal for.*XYZ$',
                                int, 'XYZ')

    or:

        with self.assertRaisesRegexp(ValueError, 'literal'):
           int('XYZ')

    New in version 3.1.

  `assertIsNone`(expr[, msg])

    This signals a test failure if expr is not None.

    New in version 3.1.

  `assertIsNotNone`(expr[, msg])

    The inverse of the `assertIsNone()` method. This signals a test failure if expr is None.

    New in version 3.1.

  `assertIs`(expr1, expr2[, msg])

    This signals a test failure if expr1 and expr2 don’t evaluate to the same object.

    New in version 3.1.

  `assertIsNot`(expr1, expr2[, msg])

    The inverse of the `assertIs()` method. This signals a test failure if expr1 and expr2 evaluate to the same object.

    New in version 3.1.

  `assertFalse`(expr[, msg])
  `failIf`(expr[, msg])

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

    Deprecated since version 3.1: `failIf()`.

  `fail`([msg])
    Signals a test failure unconditionally, with msg or `None` for the error message.
  `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`.
  `longMessage`

    If set to True then any explicit failure message you pass in to the assert methods will be appended to the end of the normal failure message. The normal messages contain useful information about the objects involved, for example the message from assertEqual shows you the repr of the two unequal objects. Setting this attribute to True allows you to have a custom error message in addition to the normal one.

    This attribute defaults to False, meaning that a custom message passed to an assert method will silence the normal message.

    The class setting can be overridden in individual tests by assigning an instance attribute to True or False before calling the assert methods.

    New in version 3.1.

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

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

  `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.
  `shortDescription`()

    Returns a 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, along with the method name.

    Changed in version 3.1: In earlier versions this only returned the first line of the test method’s docstring, if available or the `None`. That led to undesirable behavior of not printing the test name when someone was thoughtful enough to write a docstring.

  `addTypeEqualityFunc`(typeobj, function)

    Registers a type specific `assertEqual()` equality checking function to be called by `assertEqual()` when both objects it has been asked to compare are exactly typeobj (not subclasses). function must take two positional arguments and a third msg=None keyword argument just as `assertEqual()` does. It must raise `self.failureException` when inequality between the first two parameters is detected.

    One good use of custom equality checking functions for a type is to raise `self.failureException` with an error message useful for debugging the problem by explaining the inequalities in detail.

    New in version 3.1.

  `addCleanup`(function[, *args[, **kwargs]])

    Add a function to be called after `tearDown()` to cleanup resources used during the test. Functions will be called in reverse order to the order they are added (LIFO). They are called with any arguments and keyword arguments passed into `addCleanup()` when they are added.

    If `setUp()` fails, meaning that `tearDown()` is not called, then any cleanup functions added will still be called.

    New in version 2.7.

  `doCleanups`()

    This method is called uncoditionally after `tearDown()`, or after `setUp()` if `setUp()` raises an exception.

    It is responsible for calling all the cleanup functions added by `addCleanup()`. If you need cleanup functions to be called prior to `tearDown()` then you can call `doCleanups()` yourself.

    `doCleanups()` pops methods off the stack of cleanup functions one at a time, so it can be called at any time.

    New in version 2.7.

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.

### 25.3.5.2. Grouping tests

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.

  `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:

  `addTest`(test)
    Add a `TestCase` or `TestSuite` to the suite.
  `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`:

  `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.
  `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.
  `countTestCases`()
    Return the number of tests represented by this test object, including all individual tests and sub-suites.
  `__iter__`()

    Tests grouped by a `TestSuite` are always accessed by iteration. Subclasses can lazily provide tests by overriding `__iter__()`. Note that this method maybe called several times on a single suite (for example when counting tests or comparing for equality) so the tests returned must be the same for repeated iterations.

    Changed in version 2.7: In earlier versions the `TestSuite` accessed tests directly rather than through iteration, so overriding `__iter__()` wasn’t sufficient for providing tests.

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

### 25.3.5.3. Loading and running tests

class `unittest.``TestLoader`

  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:

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

    Note

    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.

  `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.

  `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.
  `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:

  `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.

  `sortTestMethodsUsing`
    Function to be used to compare method names when sorting them in `getTestCaseNames()` and all the `loadTestsFrom*()` methods.
  `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.

class `unittest.``TestResult`

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

  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:

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

    A list containing 2-tuples of `TestCase` instances and strings holding the reason for skipping the test.

    New in version 3.1.

  `expectedFailures`
    A list contaning 2-tuples of `TestCase` instances and strings holding formatted tracebacks. Each tuple represents a expected failures of the test case.
  `unexpectedSuccesses`
    A list containing `TestCase` instances that were marked as expected failures, but succeeded.
  `shouldStop`
    Set to `True` when the execution of tests should stop by `stop()`.
  `testsRun`
    The total number of tests run so far.
  `wasSuccessful`()
    Return `True` if all tests run so far have passed, otherwise returns `False`.
  `stop`()

    This method can be called to signal that the set of tests being run should be aborted by setting the `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.

  `startTest`(test)

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

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

  `stopTest`(test)

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

    The default implementation does nothing.

  `startTestRun`(test)

    Called once before any tests are executed.

    New in version 2.7.

  `stopTestRun`(test)

    Called once before any tests are executed.

    New in version 2.7.

  `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.

  `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.

  `addSuccess`(test)

    Called when the test case test succeeds.

    The default implementation does nothing.

  `addSkip`(test, reason)

    Called when the test case test is skipped. reason is the reason the test gave for skipping.

    The default implementation appends a tuple `(test, reason)` to the instance’s `skipped` attribute.

  `addExpectedFailure`(test, err)

    Called when the test case test fails, but was marked with the `expectedFailure()` decorator.

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

  `addUnexpectedSuccess`(test)

    Called when the test case test was marked with the `expectedFailure()` decorator, but succeeded.

    The default implementation appends the test to the instance’s `unexpectedSuccesses` attribute.

`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.

  `_makeResult`()
    This method returns the instance of `TestResult` used by `run()`. It is not intended to be called directly, but can be overridden in subclasses to provide a custom `TestResult`.

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

  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. By default `main` calls `sys.exit()` with an exit code indicating success or failure of the tests run.

  `main` supports being used from the interactive interpreter by passing in the argument `exit=False`. This displays the result on standard output without calling `sys.exit()`:

      >>> from unittest import main
      >>> main(module='test_module', exit=False)

  Calling `main` actually returns an instance of the `TestProgram` class. This stores the result of the tests run as the `result` attribute.

  Changed in version 2.7: The `exit` parameter was added.

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