Mock-Object provides a declarative mocking interface that results in a
very concise, but clear syntax. There are separate facilities for
mocking object instances, and classes. You can quickly create an
instance of an object with custom attributes and methods. You can also
quickly create an anonymous class, optionally inheriting from another,
with whatever methods you desire.

Mock-Object also provides a tool that provides an OO interface to
overriding methods in existing classes. This tool also allows for the
restoration of the original class methods. Best of all this is a
localized tool, when your control object falls out of scope the original
class is restored.