have_received vs. should_receive

.rspec

--color

currency_converter.rb

class ConverterService
end

class CurrencyConverter
  def initialize(yen)
    @yen = yen
  end

  def to_human_dollars
    dollars = ConverterService.yen_to_dollars(@yen)
    rounded_dollars = dollars.round
    "$#{rounded_dollars}"
  end
end

currency_converter_spec.rb

require_relative 'currency_converter'

describe CurrencyConverter do
  let(:converter) { CurrencyConverter.new(10_000) }

  describe "#to_human_dollars" do
    subject(:human_dollars) { converter.to_human_dollars }
    before { ConverterService.stub(yen_to_dollars: 100.10) }

    describe "with have_received" do
      before { human_dollars }

      it "calls the conversion service with the correct yen" do
        expect(ConverterService).to have_received(:yen_to_dollars).with(10_000)
      end

      it { should eq("$100") }
    end

    describe "with should_receive" do
      it "calls the conversion service with the correct yen" do
        ConverterService.should_receive(:yen_to_dollars).with(10_000)
        human_dollars
      end

      it { should eq("$100") }
    end
  end
end

Gemfile

source 'https://rubygems.org'

gem 'rspec'

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    diff-lcs (1.2.5)
    rspec (2.14.1)
      rspec-core (~> 2.14.0)
      rspec-expectations (~> 2.14.0)
      rspec-mocks (~> 2.14.0)
    rspec-core (2.14.7)
    rspec-expectations (2.14.4)
      diff-lcs (>= 1.1.3, < 2.0)
    rspec-mocks (2.14.4)

PLATFORMS
  ruby

DEPENDENCIES
  rspec