Set method stubs and message expectations on any instance of a class:
class Foo; end
Foo.any_instance.stub(:bar) { 'bar' }
Foo.new.bar # => 'bar'
Sets up top-level environment to explore rspec-mocks. Mostly useful in irb:
$ irb
> require 'rspec/mocks/standalone'
> foo = double()
> foo.stub(:bar) { :baz }
> foo.bar
=> :baz