Hi, I'm having some strange issue with rspec mocks and hope someone can point out what I'm doing wrong. I have a Objective C class with the method: buildRequestWithUrl:method:header:body: I wrote an rspec mock for this class. I'm setting up an expectation as follows: @requestBuilder.should_receive(:buildRequestWithUrl) .with("http://example.com", method:"POST", header:nil, body:anything() ) .and_return(nil) When the class being tested calls the aforementioned method I get the following error: RuntimeError: NSInvalidArgumentException: -[Mock buildRequestWithUrl:method:header:body:]: unrecognized selector sent to instance 0x200373ea0 I set the expectations for another method of the same class called :queryStringForDictionary In this case the expectation and call do work. @requestBuilder.should_receive(:queryStringForDictionary).and_return( body ) In another project I'm calling the same class from ruby code and there the mocks and expectations do work properly. In this Objective C project they don't. Thanks in advance, Gabriel Ayuso