Rspec-rails is a rails plugin which brings the Rspec Ruby Behaviour Driven Development framework to rails along with some rails specific helpers. One of these hugely useful helper functions is:

mock_model(model_class, options_and_stubs = {})

This creates a mock object with the common methods stubbed out. It also allows you to specify other methods you want to stub.

You can use Rspec with a number of mocking frameworks (Rspec 1.1.5: mocha, flexmock & RR). Unfortunately the Rspec-rails mock_model helper is not compatible with the RR test double framework.
It throws this error message:

undefined method `to_sym' for {:count=>0}:Hash

as it uses a stub function:

:errors => stub("errors", :count => 0)

which does not match RR’s stub method.

I’ve written a patch which will allow mock_model to work with RR. Note: It’s still a work in progress but I am using it successfully in a number of projects.

You can get the latest code from GitHub:
git clone git://github.com/josephwilk/rspec-rr.git

1. Spec::Rails::Mocks.module_eval do
2.  
3. # Creates a mock object instance for a +model_class+ with common
4. # methods stubbed out. Additional methods may be easily stubbed (via
5. # add_stubs) if +stubs+ is passed.
6. def mock_model(model_class, options_and_stubs = {})
7. m = model_class.new
8. id = next_id
9.  
10. # our equivalent to Rspecs :errors => ''# stub("errors", :count => 0)
11. stub(errors_stub = Object.new).count{0}
12.  
13. options_and_stubs.reverse_merge!({
14. :id => id,
15. :to_param => "#{id}",
16. :new_record? => false,
17. :errors => errors_stub
18. })
19.  
20. options_and_stubs.each do |method,value|
21. eval "stub(m).#{method}{value}"
22. end
23.  
24. yield m if block_given?
25. m
26. end
27.  
28. end