mox3/mox3/stubout.py

# 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
#
#      http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# This is a fork of the pymox library intended to work with Python 3.
# The file was modified by quermit@gmail.com and dawid.fatyga@gmail.com

import inspect


class StubOutForTesting(object):
    """Sample Usage:

       You want os.path.exists() to always return true during testing.

       stubs = StubOutForTesting()
       stubs.Set(os.path, 'exists', lambda x: 1)
           ...
       stubs.UnsetAll()

       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):
        self.SmartUnsetAll()
        self.UnsetAll()

    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.

        Notes:
          - 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 setattr()).

        Raises AttributeError if the attribute cannot be found.
        """
        if (inspect.ismodule(obj) or
                (not inspect.isclass(obj) and attr_name in obj.__dict__)):
            orig_obj = obj
            orig_attr = getattr(obj, attr_name)

        else:
            if not inspect.isclass(obj):
                mro = list(inspect.getmro(obj.__class__))
            else:
                mro = list(inspect.getmro(obj))

            mro.reverse()

            orig_attr = None

            for cls in mro:
                try:
                    orig_obj = cls
                    orig_attr = getattr(obj, attr_name)
                except AttributeError:
                    continue

        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.

        Restores things to their original definition. Its okay to call
        SmartUnsetAll() repeatedly, as later calls have no effect if no
        SmartSet() calls have been made.
        """
        self.stubs.reverse()

        for args in self.stubs:
            setattr(*args)

        self.stubs = []

    def Set(self, parent, child_name, new_child):
        """Replace child_name's old definition with new_child.

        Replace definiion 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.__func__)

        self.cache.append((parent, old_child, child_name))
        setattr(parent, child_name, new_child)

    def UnsetAll(self):
        """Reverses all the Set() calls.

        Restores 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)
        self.cache.reverse()

        for (parent, old_child, child_name) in self.cache:
            setattr(parent, child_name, old_child)
        self.cache = []