RSpec Stubbing: Return the parameter

Question

Though my question is pretty straightforward, I failed to find an answer around here:

How can I stub a method and return the parameter itself (for example on a method that does an array-operation)?

Something like this:

 interface.stub!(:get_trace).with(<whatever_here>).and_return(<whatever_here>)

Answer 1

Note: The stub method has been deprecated. Please see this answer for the modern way to do this.

---

stub! can accept a block. The block receives the parameters; the return value of the block is the return value of the stub:

class Interface
end

describe Interface do
  it "should have a stub that returns its argument" do
    interface = Interface.new
    interface.stub!(:get_trace) do |arg|
      arg
    end
    interface.get_trace(123).should eql 123
  end
end