class unittest.TestCase(methodName='runTest')
Instances of the TestCase
class represent the logical test 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 tests, 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 base method: the method named methodName. In most uses of TestCase
, you will neither change the methodName nor reimplement the default runTest()
method.
Changed in version 3.2: TestCase
can be instantiated successfully without providing a methodName. This makes it easier to experiment with TestCase
from the interactive interpreter.
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; other than
AssertionError
orSkipTest
, 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, other than
AssertionError
orSkipTest
, raised by this method will be considered an additional error rather than a test failure (thus increasing the total number of reported errors). This method will only be called if thesetUp()
succeeds, regardless of the outcome of the test method. The default implementation does nothing.
-
setUpClass()
-
A class method called before tests in an individual class run.
setUpClass
is called with the class as the only argument and must be decorated as aclassmethod()
:@classmethod def setUpClass(cls): ...
See Class and Module Fixtures for more details.
New in version 3.2.
-
tearDownClass()
-
A class method called after tests in an individual class have run.
tearDownClass
is called with the class as the only argument and must be decorated as aclassmethod()
:@classmethod def tearDownClass(cls): ...
See Class and Module Fixtures for more details.
New in version 3.2.
-
run(result=None)
-
Run the test, collecting the result into the
TestResult
object passed as result. If result is omitted orNone
, a temporary result object is created (by calling thedefaultTestResult()
method) and used. The result object is returned torun()
‘s caller.The same effect may be had by simply calling the
TestCase
instance.Changed in version 3.3: Previous versions of
run
did not return the result. Neither did calling an instance.
-
skipTest(reason)
-
Calling this during a test method or
setUp()
skips the current test. See Skipping tests and expected failures for more information.New in version 3.1.
-
subTest(msg=None, **params)
-
Return a context manager which executes the enclosed code block as a subtest. msg and params are optional, arbitrary values which are displayed whenever a subtest fails, allowing you to identify them clearly.
A test case can contain any number of subtest declarations, and they can be arbitrarily nested.
See Distinguishing test iterations using subtests for more information.
New in version 3.4.
-
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 TestCase
class provides several assert methods to check for and report failures. The following table lists the most commonly used methods (see the tables below for more assert methods):
Method | Checks that | New in |
---|---|---|
assertEqual(a, b) | a == b | |
assertNotEqual(a, b) | a != b | |
assertTrue(x) | bool(x) is True | |
assertFalse(x) | bool(x) is False | |
assertIs(a, b) | a is b | 3.1 |
assertIsNot(a, b) | a is not b | 3.1 |
assertIsNone(x) | x is None | 3.1 |
assertIsNotNone(x) | x is not None | 3.1 |
assertIn(a, b) | a in b | 3.1 |
assertNotIn(a, b) | a not in b | 3.1 |
assertIsInstance(a, b) | isinstance(a, b) | 3.2 |
assertNotIsInstance(a, b) | not isinstance(a, b) | 3.2 |
All the assert methods accept a msg argument that, if specified, is used as the error message on failure (see also longMessage
). Note that the msg keyword argument can be passed to assertRaises()
, assertRaisesRegex()
, assertWarns()
, assertWarnsRegex()
only when they are used as a context manager.
-
assertEqual(first, second, msg=None)
-
Test that first and second are equal. If the values do not compare equal, the test will fail.
In addition, if first and second are the exact same type and one of list, tuple, dict, set, frozenset or str or any type that a subclass registers with
addTypeEqualityFunc()
the type-specific equality function will be called in order to generate a more useful default error message (see also the list of type-specific methods).Changed in version 3.1: Added the automatic calling of type-specific equality function.
Changed in version 3.2:
assertMultiLineEqual()
added as the default type equality function for comparing strings.
-
assertNotEqual(first, second, msg=None)
-
Test that first and second are not equal. If the values do compare equal, the test will fail.
-
assertTrue(expr, msg=None)
-
assertFalse(expr, msg=None)
-
Test that expr is true (or false).
Note that this is equivalent to
bool(expr) is True
and not toexpr is True
(useassertIs(expr, True)
for the latter). This method should also be avoided when more specific methods are available (e.g.assertEqual(a, b)
instead ofassertTrue(a == b)
), because they provide a better error message in case of failure.
-
assertIs(first, second, msg=None)
-
assertIsNot(first, second, msg=None)
-
Test that first and second evaluate (or don’t evaluate) to the same object.
New in version 3.1.
-
assertIsNone(expr, msg=None)
-
assertIsNotNone(expr, msg=None)
-
Test that expr is (or is not) None.
New in version 3.1.
-
assertIn(first, second, msg=None)
-
assertNotIn(first, second, msg=None)
-
Test that first is (or is not) in second.
New in version 3.1.
-
assertIsInstance(obj, cls, msg=None)
-
assertNotIsInstance(obj, cls, msg=None)
-
Test that obj is (or is not) an instance of cls (which can be a class or a tuple of classes, as supported by
isinstance()
). To check for the exact type, useassertIs(type(obj), cls)
.New in version 3.2.
It is also possible to check the production of exceptions, warnings, and log messages using the following methods:
Method | Checks that | New in |
---|---|---|
assertRaises(exc, fun, *args, **kwds) |
fun(*args, **kwds) raises exc
| |
assertRaisesRegex(exc, r, fun, *args, **kwds) |
fun(*args, **kwds) raises exc and the message matches regex r
| 3.1 |
assertWarns(warn, fun, *args, **kwds) |
fun(*args, **kwds) raises warn
| 3.2 |
assertWarnsRegex(warn, r, fun, *args, **kwds) |
fun(*args, **kwds) raises warn and the message matches regex r
| 3.2 |
assertLogs(logger, level) | The with block logs on logger with minimum level
| 3.4 |
-
assertRaises(exception, callable, *args, **kwds)
-
assertRaises(exception, msg=None)
-
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 only the exception and possibly the msg arguments are given, return a context manager so that the code under test can be written inline rather than as a function:
with self.assertRaises(SomeException): do_something()
When used as a context manager,
assertRaises()
accepts the additional keyword argument msg.The context manager will store the caught exception object in its
exception
attribute. This can be useful if the intention is to perform additional checks on the exception raised:with self.assertRaises(SomeException) as cm: do_something() the_exception = cm.exception self.assertEqual(the_exception.error_code, 3)
Changed in version 3.1: Added the ability to use
assertRaises()
as a context manager.Changed in version 3.2: Added the
exception
attribute.Changed in version 3.3: Added the msg keyword argument when used as a context manager.
-
assertRaisesRegex(exception, regex, callable, *args, **kwds)
-
assertRaisesRegex(exception, regex, msg=None)
-
Like
assertRaises()
but also tests that regex matches on the string representation of the raised exception. regex may be a regular expression object or a string containing a regular expression suitable for use byre.search()
. Examples:self.assertRaisesRegex(ValueError, "invalid literal for.*XYZ'$", int, 'XYZ')
or:
with self.assertRaisesRegex(ValueError, 'literal'): int('XYZ')
New in version 3.1: under the name
assertRaisesRegexp
.Changed in version 3.2: Renamed to
assertRaisesRegex()
.Changed in version 3.3: Added the msg keyword argument when used as a context manager.
-
assertWarns(warning, callable, *args, **kwds)
-
assertWarns(warning, msg=None)
-
Test that a warning is triggered when callable is called with any positional or keyword arguments that are also passed to
assertWarns()
. The test passes if warning is triggered and fails if it isn’t. Any exception is an error. To catch any of a group of warnings, a tuple containing the warning classes may be passed as warnings.If only the warning and possibly the msg arguments are given, return a context manager so that the code under test can be written inline rather than as a function:
with self.assertWarns(SomeWarning): do_something()
When used as a context manager,
assertWarns()
accepts the additional keyword argument msg.The context manager will store the caught warning object in its
warning
attribute, and the source line which triggered the warnings in thefilename
andlineno
attributes. This can be useful if the intention is to perform additional checks on the warning caught:with self.assertWarns(SomeWarning) as cm: do_something() self.assertIn('myfile.py', cm.filename) self.assertEqual(320, cm.lineno)
This method works regardless of the warning filters in place when it is called.
New in version 3.2.
Changed in version 3.3: Added the msg keyword argument when used as a context manager.
-
assertWarnsRegex(warning, regex, callable, *args, **kwds)
-
assertWarnsRegex(warning, regex, msg=None)
-
Like
assertWarns()
but also tests that regex matches on the message of the triggered warning. regex may be a regular expression object or a string containing a regular expression suitable for use byre.search()
. Example:self.assertWarnsRegex(DeprecationWarning, r'legacy_function\(\) is deprecated', legacy_function, 'XYZ')
or:
with self.assertWarnsRegex(RuntimeWarning, 'unsafe frobnicating'): frobnicate('/etc/passwd')
New in version 3.2.
Changed in version 3.3: Added the msg keyword argument when used as a context manager.
-
assertLogs(logger=None, level=None)
-
A context manager to test that at least one message is logged on the logger or one of its children, with at least the given level.
If given, logger should be a
logging.Logger
object or astr
giving the name of a logger. The default is the root logger, which will catch all messages.If given, level should be either a numeric logging level or its string equivalent (for example either
"ERROR"
orlogging.ERROR
). The default islogging.INFO
.The test passes if at least one message emitted inside the
with
block matches the logger and level conditions, otherwise it fails.The object returned by the context manager is a recording helper which keeps tracks of the matching log messages. It has two attributes:
-
records
-
A list of
logging.LogRecord
objects of the matching log messages.
-
output
-
A list of
str
objects with the formatted output of matching messages.
Example:
with self.assertLogs('foo', level='INFO') as cm: logging.getLogger('foo').info('first message') logging.getLogger('foo.bar').error('second message') self.assertEqual(cm.output, ['INFO:foo:first message', 'ERROR:foo.bar:second message'])
New in version 3.4.
-
There are also other methods used to perform more specific checks, such as:
Method | Checks that | New in |
---|---|---|
assertAlmostEqual(a, b) | round(a-b, 7) == 0 | |
assertNotAlmostEqual(a, b) | round(a-b, 7) != 0 | |
assertGreater(a, b) | a > b | 3.1 |
assertGreaterEqual(a, b) | a >= b | 3.1 |
assertLess(a, b) | a < b | 3.1 |
assertLessEqual(a, b) | a <= b | 3.1 |
assertRegex(s, r) | r.search(s) | 3.1 |
assertNotRegex(s, r) | not r.search(s) | 3.2 |
assertCountEqual(a, b) | a and b have the same elements in the same number, regardless of their order | 3.2 |
-
assertAlmostEqual(first, second, places=7, msg=None, delta=None)
-
assertNotAlmostEqual(first, second, places=7, msg=None, delta=None)
-
Test that first and second are approximately (or not approximately) equal by computing the difference, rounding to the given number of decimal places (default 7), and comparing to zero. Note that these methods round the values to the given number of decimal places (i.e. like the
round()
function) and not significant digits.If delta is supplied instead of places then the difference between first and second must be less or equal to (or greater than) delta.
Supplying both delta and places raises a
TypeError
.Changed in version 3.2:
assertAlmostEqual()
automatically considers almost equal objects that compare equal.assertNotAlmostEqual()
automatically fails if the objects compare equal. Added the delta keyword argument.
-
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:
>>> self.assertGreaterEqual(3, 4) AssertionError: "3" unexpectedly not greater than or equal to "4"
New in version 3.1.
-
assertRegex(text, regex, msg=None)
-
assertNotRegex(text, regex, msg=None)
-
Test that a regex search matches (or does not match) text. In case of failure, the error message will include the pattern and the text (or the pattern and the part of text that unexpectedly matched). regex may be a regular expression object or a string containing a regular expression suitable for use by
re.search()
.New in version 3.1: under the name
assertRegexpMatches
.Changed in version 3.2: The method
assertRegexpMatches()
has been renamed toassertRegex()
.New in version 3.2:
assertNotRegex()
.
-
assertCountEqual(first, second, msg=None)
-
Test that sequence first contains the same elements as second, regardless of their order. When they don’t, an error message listing the differences between the sequences will be generated.
Duplicate elements are not ignored when comparing first and second. It verifies whether each element has the same count in both sequences. Equivalent to:
assertEqual(Counter(list(first)), Counter(list(second)))
but works with sequences of unhashable objects as well.New in version 3.2.
The assertEqual()
method dispatches the equality check for objects of the same type to different type-specific methods. These methods are already implemented for most of the built-in types, but it’s also possible to register new methods using addTypeEqualityFunc()
:
-
addTypeEqualityFunc(typeobj, function)
-
Registers a type-specific method called by
assertEqual()
to check if two objects of exactly the same typeobj (not subclasses) compare equal. function must take two positional arguments and a third msg=None keyword argument just asassertEqual()
does. It must raiseself.failureException(msg)
when inequality between the first two parameters is detected – possibly providing useful information and explaining the inequalities in details in the error message.New in version 3.1.
The list of type-specific methods automatically used by assertEqual()
are summarized in the following table. Note that it’s usually not necessary to invoke these methods directly.
Method | Used to compare | New in |
---|---|---|
assertMultiLineEqual(a, b) | strings | 3.1 |
assertSequenceEqual(a, b) | sequences | 3.1 |
assertListEqual(a, b) | lists | 3.1 |
assertTupleEqual(a, b) | tuples | 3.1 |
assertSetEqual(a, b) | sets or frozensets | 3.1 |
assertDictEqual(a, b) | dicts | 3.1 |
-
assertMultiLineEqual(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. This method is used by default when comparing strings with
assertEqual()
.New in version 3.1.
-
assertSequenceEqual(first, second, msg=None, seq_type=None)
-
Tests that two sequences are equal. If a seq_type is supplied, both first and second 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.
This method is not called directly by
assertEqual()
, but it’s used to implementassertListEqual()
andassertTupleEqual()
.New in version 3.1.
-
assertListEqual(first, second, msg=None)
-
assertTupleEqual(first, second, 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. These methods are used by default when comparing lists or tuples with
assertEqual()
.New in version 3.1.
-
assertSetEqual(first, second, msg=None)
-
Tests that two sets are equal. If not, an error message is constructed that lists the differences between the sets. This method is used by default when comparing sets or frozensets with
assertEqual()
.Fails if either of first or second does not have a
set.difference()
method.New in version 3.1.
-
assertDictEqual(first, second, msg=None)
-
Test that two dictionaries are equal. If not, an error message is constructed that shows the differences in the dictionaries. This method will be used by default to compare dictionaries in calls to
assertEqual()
.New in version 3.1.
Finally the TestCase
provides the following methods and attributes:
-
fail(msg=None)
-
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 toTrue
allows you to have a custom error message in addition to the normal one.This attribute defaults to
True
. If set to False then 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
orFalse
before calling the assert methods.New in version 3.1.
-
maxDiff
-
This attribute controls the maximum length of diffs output by assert methods that report diffs on failure. It defaults to 80*8 characters. Assert methods affected by this attribute are
assertSequenceEqual()
(including all the sequence comparison methods that delegate to it),assertDictEqual()
andassertMultiLineEqual()
.Setting
maxDiff
to None means that there is no maximum length of diffs.New in version 3.2.
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 be1
.
-
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 ofTestResult
; subclasses ofTestCase
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, orNone
.Changed in version 3.1: In 3.1 this was changed to add the test name to the short description even in the presence of a docstring. This caused compatibility issues with unittest extensions and adding the test name was moved to the
TextTestResult
in Python 3.2.
-
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 intoaddCleanup()
when they are added.If
setUp()
fails, meaning thattearDown()
is not called, then any cleanup functions added will still be called.New in version 3.1.
-
doCleanups()
-
This method is called unconditionally after
tearDown()
, or aftersetUp()
ifsetUp()
raises an exception.It is responsible for calling all the cleanup functions added by
addCleanup()
. If you need cleanup functions to be called prior totearDown()
then you can calldoCleanups()
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 3.1.
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