Question

I’d like to have instance methods of a class return self, and be init with another class instance self.
However I’m struggling to see how to spec this succintly:

::Api.should_receive(:new).once do |arg|
  arg.should be_an_instance_of(::Cli)
end

When running this spec, this ensures that the next method is called on true instead of the Api instance, as expected, that is the return value of the block. Example:

class Cli
  def eg
    api = Api.new(self)
    api.blowup # undefined method for true
  end
end

I’d really like the block to return the Api instance self without invoking another call to Api.new(...) in the spec, the example below does this and to my mind a non-rspec reader would wonder why the spec passes when clearly Api.new(...) has been called more than once.

Can anyone suggest how best to do this?

Current solution:
This reads like ::Api.new(...) is called thrice: once to create api, once to create cli, once to create start. Yet the spec of one call passes. I understand why and that this is correct, so not a bug. However I’d like a spec that a reader not familiar with rspec could scan and not have the impression that Api.new has been called more than once. Also note that ...once.and_return(api){...} does not work, the block needs to return api in order to pass.

let(:cli){ ::Cli.start(['install']) }
let(:start){ ::Cli.start(['install']) }
it 'is the API' do
  api = ::Api.new(cli)
  ::Api.should_receive(:new).once do |arg|
    arg.should be_an_instance_of(::Cli)
    api
  end
  start
end

Answer 1

You can save the original method (new) in a local variable and then use it to return the new api from within the block:

original_method = ::Api.method(:new)
::Api.should_receive(:new).once do |arg|
  arg.should be_an_instance_of(::Cli)
  original_method.call(arg)
end

This will run the expectation, checking that the argument is an instance of ::Cli, and then return the value from the original method (i.e. the api).