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# Copyright 2008 Google Inc.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.
import inspect
class StubOutForTesting:
"""Sample Usage:
You want os.path.exists() to always return true during testing.
stubs = StubOutForTesting()
stubs.Set(os.path, 'exists', lambda x: 1)
The above changes os.path.exists into a lambda that returns 1. Once
the ... part of the code finishes, the UnsetAll() looks up the old value
of os.path.exists and restores it.
def __init__(self):
self.cache = []
self.stubs = []
def __del__(self):
def SmartSet(self, obj, attr_name, new_attr):
"""Replace obj.attr_name with new_attr. This method is smart and works
at the module, class, and instance level while preserving proper
inheritance. It will not stub out C types however unless that has been
explicitly allowed by the type.
This method supports the case where attr_name is a staticmethod or a
classmethod of obj.
- If obj is an instance, then it is its class that will actually be
stubbed. Note that the method Set() does not do that: if obj is
an instance, it (and not its class) will be stubbed.
- The stubbing is using the builtin getattr and setattr. So, the __get__
and __set__ will be called when stubbing (TODO: A better idea would
probably be to manipulate obj.__dict__ instead of getattr() and
Raises AttributeError if the attribute cannot be found.
if (inspect.ismodule(obj) or
(not inspect.isclass(obj) and obj.__dict__.has_key(attr_name))):
orig_obj = obj
orig_attr = getattr(obj, attr_name)
if not inspect.isclass(obj):
mro = list(inspect.getmro(obj.__class__))
mro = list(inspect.getmro(obj))
orig_attr = None
for cls in mro:
orig_obj = cls
orig_attr = getattr(obj, attr_name)
except AttributeError:
if orig_attr is None:
raise AttributeError("Attribute not found.")
# Calling getattr() on a staticmethod transforms it to a 'normal' function.
# We need to ensure that we put it back as a staticmethod.
old_attribute = obj.__dict__.get(attr_name)
if old_attribute is not None and isinstance(old_attribute, staticmethod):
orig_attr = staticmethod(orig_attr)
self.stubs.append((orig_obj, attr_name, orig_attr))
setattr(orig_obj, attr_name, new_attr)
def SmartUnsetAll(self):
"""Reverses all the SmartSet() calls, restoring things to their original
definition. Its okay to call SmartUnsetAll() repeatedly, as later calls
have no effect if no SmartSet() calls have been made.
for args in self.stubs:
self.stubs = []
def Set(self, parent, child_name, new_child):
"""Replace child_name's old definition with new_child, in the context
of the given parent. The parent could be a module when the child is a
function at module scope. Or the parent could be a class when a class'
method is being replaced. The named child is set to new_child, while
the prior definition is saved away for later, when UnsetAll() is called.
This method supports the case where child_name is a staticmethod or a
classmethod of parent.
old_child = getattr(parent, child_name)
old_attribute = parent.__dict__.get(child_name)
if old_attribute is not None:
if isinstance(old_attribute, staticmethod):
old_child = staticmethod(old_child)
elif isinstance(old_attribute, classmethod):
old_child = classmethod(old_child.im_func)
self.cache.append((parent, old_child, child_name))
setattr(parent, child_name, new_child)
def UnsetAll(self):
"""Reverses all the Set() calls, restoring things to their original
definition. Its okay to call UnsetAll() repeatedly, as later calls have
no effect if no Set() calls have been made.
# Undo calls to Set() in reverse order, in case Set() was called on the
# same arguments repeatedly (want the original call to be last one undone)
for (parent, old_child, child_name) in self.cache:
setattr(parent, child_name, old_child)
self.cache = []