How to stub method on instance variable?

Question

So I have this simple ruby class:

class GetRequestList
  def initialize(current_user, filter_hash)
    @authorizer = RequestAuthorizer.new(current_user)
    @filter    = RequestFilter.new(filter_hash)
  end
  def generate
    Request.send_chain(@authorizer.method_chain)
           .send_chain(@filter.method_chain)
  end
end

And I want to test that Request receives two send_chain methods in isolation of RequestAuthorizer and RequestFilter implementations. To do that I'm trying to use some stubs:

require 'test_helper'

class GetRequestListTest < ActiveSupport::TestCase

  test "request should be filtered by filter and role" do
    Request.expects(:send_chain).twice.returns([build(:request)])
    RequestFilter.stubs(:new)
    RequestFilter.any_instance.stubs(:method_chain).returns([])
    RequestAuthorizer.stubs(:new)
    RequestAuthorizer.any_instance.stubs(:method_chain).returns([])
    assert GetRequestList.new(:current_user, :filter).generate.size == 1
  end
end

You see what is wrong. stubs(:new) returns nil and there is no instances of RequestAuthorizer and RequestFilter in instance variables of GetRequestList and we get an error. I can't figure out how to stub methods on instance variables. Any suggestions?

Answer 1

Instead of stubbing out new to return no value, have it return something e.g.

mock_request_filter = mock()
RequestFilter.stubs(:new).returns(mock_filter)

This also enables you to get read of the stubs on any_instance - just set them on mock_request_filter instead.