From: Jim Weirich <jim@...>
Date: 2006-03-21T00:57:50+09:00
Subject: Re: Library for Mocking

Thiago Arrais wrote:
> Rubysts,
> 
> I am looking for a library for mocking objects.
[...]
> FlexMock works by creating a full-blown, ready-to-use, suited-to-your
> needs mock object in one method call (namely FlexMock.use). Then you
> can just inject it into your tested object and use it.

Actually, you still need to specify the behavior of the mock.  The "use" 
module method just ensures that that mock_verify is properly called at 
the end of the test.

FlexMock currently has two ways of specifying behavior:  (1) the 
original "mock_handles" way and (2) the JMock-like "should_receive" way.

> [...] I prefer the record/playback
> metaphor, where you actually call the methods you want to be called on
> the record phase and then the object under test is responsible for
> making the expected calls on playback phase. 

Currently, FlexMock does not support a recording mode.  But one could 
easily be added:

  class FlexMock
    class Recorder
      def initialize(mock)
        @mock = mock
      end
      def method_missing(sym, *args, &block)
        @mock.should_receive(sym).and_return(&block)
      end
    end

    def should_expect
      yield Recorder.new(self)
    end
  end

This allows you to do the following:

  FlexMock.use("socket") do |mock_socket|
    mock_socket.should_expect do |recording_socket|
      recording_socket.addr { ["AF_INET", 23, "localhost", "127.0.0.1"] 
}
      recording_socket.getsocketopt { DEFAULT_SOCKET_OPTS }
    end

    # Testing code goes here that uses mock_socket and
    # calls addr and getsocketopt.
  end

There are some open questions.

(1) how are arguments to the mock method validated? (exact match, 
constraints, no validation?)

(2) is the order of the messages important?

The implementation provided above does no argument validation (but the 
arguments are sent to the recording block for hand validation) and the 
order of method calls is ignored.  However, I think automatic parameter 
validation could be added without too much effort.

If there is sufficient interest in a recording interface to MockFlex, I 
am willing to consider it for inclusion in the library.

--
-- Jim Weirich

-- 
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