Lib/unittest/case.py (part 5)

Source:

cpython 3.14 @ ab2d84fe1023/Lib/unittest/case.py ↗

This annotation covers exception and warning assertion context managers. See lib_unittest4_detail for assertEqual, assertIn, subTest, and addCleanup.

Map

Lines	Symbol	Role
1-80	assertRaises	Assert that a callable raises an exception
81-160	_AssertRaisesContext	Context manager backing assertRaises
161-240	assertRaisesRegex	Assert exception message matches a pattern
241-340	assertWarns	Assert that a warning is issued
341-500	assertLogs	Capture and assert log output

Reading

assertRaises

# CPython: Lib/unittest/case.py:740 TestCase.assertRaises
def assertRaises(self, expected_exception, *args, **kwargs):
    context = _AssertRaisesContext(expected_exception, self)
    try:
        return context.handle('assertRaises', args, kwargs)
    except self.failureException:
        raise

assertRaises can be used as a context manager (with self.assertRaises(ValueError):) or as a direct call (self.assertRaises(ValueError, func, arg)). In direct-call mode, handle calls func(*args, **kwargs) inside the context.

_AssertRaisesContext

# CPython: Lib/unittest/case.py:180 _AssertRaisesContext
class _AssertRaisesContext(_AssertRaisesBaseContext):
    def __exit__(self, exc_type, exc_value, tb):
        if exc_type is None:
            # No exception raised
            try:
                exc_name = self.expected.__name__
            except AttributeError:
                exc_name = str(self.expected)
            raise self.test_case.failureException(
                f"{exc_name} not raised")
        if not issubclass(exc_type, self.expected):
            return False  # re-raise unexpected exceptions
        self.exception = exc_value.with_traceback(None)
        return True  # suppress expected exception

Returning True from __exit__ suppresses the exception. exc_value.with_traceback(None) stores the exception without the traceback to avoid reference cycles.

assertRaisesRegex

# CPython: Lib/unittest/case.py:790 TestCase.assertRaisesRegex
def assertRaisesRegex(self, expected_exception, expected_regex, *args, **kwargs):
    context = _AssertRaisesContext(expected_exception, self, expected_regex)
    return context.handle('assertRaisesRegex', args, kwargs)

# CPython: Lib/unittest/case.py:200 _AssertRaisesContext.__exit__ (regex check)
if self.expected_regex is not None:
    expected_regex = self.expected_regex
    if not expected_regex.search(str(exc_value)):
        raise self.test_case.failureException(
            f'"{expected_regex.pattern}" does not match "{exc_value}"')

assertRaisesRegex adds a regex check on the exception message after verifying the exception type.

assertLogs

# CPython: Lib/unittest/case.py:880 TestCase.assertLogs
def assertLogs(self, logger=None, level=None):
    return _AssertLogsContext(self, logger_name=logger, level=level, no_logs=False)

# CPython: Lib/unittest/case.py:280 _AssertLogsContext.__exit__
def __exit__(self, exc_type, exc_value, tb):
    self.logger.handlers = self.old_handlers
    self.logger.propagate = self.old_propagate
    self.logger.setLevel(self.old_level)
    if exc_type is not None:
        return False
    if len(self.watcher.records) == 0:
        raise AssertionError(f"no logs of level {self.level_name} or above "
                             f"triggered on {self.logger.name}")

with self.assertLogs('mymodule', level='WARNING') as cm: installs a capturing handler on the named logger. After the block, cm.output is a list of "LEVEL:logger:message" strings.

gopy notes

assertRaises is module/unittest.AssertRaises in module/unittest/case.go. _AssertRaisesContext.__exit__ checks objects.IsInstance for the expected type. assertLogs uses module/logging.CapturingHandler to intercept log records.