Mock object implementation.

This mock object implementation is meant to be very forgiving - it returns a
new child Mock Object for every attribute accessed, and a mock object is
returned from every method call.

It is the tester's job to enable the calls that they are interested in
testing, all calls where the return value of the call and side effects are not
recorded (logging, for example) are likely to succeed w/o effort.

If you wish to call the actual implementation of a function on a MockObject,
you have to enable it using enableMethod.  If you wish to use an actual
variable setting, you need to set it.

All enabling/checking methods for a MockObject are done through the _mock
attribute.  Example:

class Foo(object):
    def __init__(self):
        # NOTE: this initialization is not called by default with the mock
        # object.
        self.one = 'a'
        self.two = 'b'

    def method(self, param):
        # this method is enabled by calling _mock.enableMethod
        param.bar('print some data')
        self.print_me('some other data', self.one)
        return self.two

    def print_me(self, other_param):
        # this method is not enabled and so is stubbed out in the MockInstance.
        print other_param

def test():
    m = MockInstance(Foo)
    m._mock.raw.two = 123
    m._mock.enable_method('method')
    param = MockObject()
    rv = m.method(param)
    assert(rv == 123) #m.two is returned
    # note that param.bar is created on the fly as it is accessed, and 
    # stores how it was called.
    assert(param.bar._mock.record.assert_called('print some data')
    # m.one and m.print_me were created on the fly as well
    # m.print_me remembers how it was called.
    m.print_me._mock.assert_called('some other data', m.one)
    # attribute values are generated on the fly but are retained between
    # accesses.
    assert(m.foo is m.foo)