from contextlib import contextmanager
from functools import wraps
from typing import Union, Type, Callable
from testfixtures import diff, compare
ExceptionOrType = Union[Exception, Type[Exception]]
param_docs = """
:param exception: This can be one of the following:
* `None`, indicating that an exception must be
raised, but the type is unimportant.
* An exception class, indicating that the type
of the exception is important but not the
parameters it is created with.
* An exception instance, indicating that an
exception exactly matching the one supplied
should be raised.
:param unless: Can be passed a boolean that, when ``True`` indicates that
no exception is expected. This is useful when checking
that exceptions are only raised on certain versions of
Python.
"""
class ShouldRaise(object):
__doc__ = """
This context manager is used to assert that an exception is raised
within the context it is managing.
""" + param_docs
#: The exception captured by the context manager.
#: Can be used to inspect specific attributes of the exception.
raised = None
def __init__(self, exception: ExceptionOrType = None, unless: bool = False):
self.exception = exception
self.expected = not unless
def __enter__(self):
return self
def __exit__(self, type_, actual, traceback):
__tracebackhide__ = True
self.raised = actual
if self.expected:
if self.exception:
if actual is not None:
if isinstance(self.exception, type):
actual = type(actual)
if self.exception is not actual:
return False
else:
if type(self.exception) is not type(actual):
return False
compare(self.exception,
actual,
x_label='expected',
y_label='raised')
elif not actual:
raise AssertionError('No exception raised!')
elif actual:
return False
return True
class should_raise:
__doc__ = """
A decorator to assert that the decorated function will raised
an exception. An exception class or exception instance may be
passed to check more specifically exactly what exception will be
raised.
""" + param_docs
def __init__(self, exception: ExceptionOrType = None, unless: bool = None):
self.exception = exception
self.unless = unless
def __call__(self, target: Callable) -> Callable:
@wraps(target)
def _should_raise_wrapper(*args, **kw):
with ShouldRaise(self.exception, self.unless):
target(*args, **kw)
return _should_raise_wrapper
@contextmanager
def ShouldAssert(expected_text: str):
"""
A context manager to check that an :class:`AssertionError`
is raised and its text is as expected.
"""
try:
yield
except AssertionError as e:
actual_text = str(e)
if expected_text != actual_text:
raise AssertionError(diff(expected_text, actual_text,
x_label='expected', y_label='actual'))
else:
raise AssertionError('Expected AssertionError(%r), None raised!' %
expected_text)
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