I was working on tests for blender when I came upon a need to mock or stub a back-tick operator e.g.:

`shell command`

Apparently this is just a shortcut for calling Kernel method :`.

So the mocking should probably be easier with Rspec mocks or mocha. something like that (didn’t test, see below):

@obj.should_receive(:`, "shell command").and_return("....")

But the problem was that I’m using RR. And RR uses a much more succinct and easy to use syntax but in this particular case it was a problem. Consider this:

# This doesn't work. it stubs the :send, not the :`
stub(@obj).send(:`, "shell command") { "...." }

RR has an instance_eval syntax, but with it I don’t know how to pass a block to the back-ticks call:

stub(@obj) do
  `shell command` { "...." } # invalid syntax here ;).
end

So after some digging inside RR’s sources I got the following working:

stub(@obj).
  __double_definition_create__.
    call(:`, "shell command") { "...." }