Method Mocking

In Rspec, I have always understood mocks/stubs to be the same thing.

I still kind of understand them to be the same, except I learned that you can force method to return a specific value; which is great for E2E testing.

For example, if you have a process that takes 5 steps and you want to test it end-to-end ..

class MyClass
  def multi_step_process
    result1 = do_step1
    result2 = do_step2(result1)
    result3 = do_step3(result2)
    result4 = do_step4(result3)
    do_step5(result4)
  end

  def do_step1 
  def do_step2 
  ...
  def do_step5
    ... 
  end
end

 

Step 1 is likely some kind of sourcing step. Find me all the records that need to be processed. You can imagine that you want tests on do_step#, but also on my_multistep_process. But how can you do that if step1 changes?

One option is to force some input into result1.

it "verify multi_step_process works e2e" do
  result1 = stub_step1_result
  result2 = do_step2(result1)
  result3 = do_step3(result2)
  result4 = do_step4(result3)
  expect(do_step5(result4)).to eq("some expected value")
end

 

This might not always work for you though. In those cases you can use the allow syntax for Rspec. For example, you need to consistenly make sure the logic in your test is the same as is in multi_step_process

it "verify multi_step_process works e2e" do
  allow(MyClass).to receive(:do_step1).and_return(stub_step1_result)
  expect(multi_step_process).to eq("some expected value")
end

This is super elegant and exactly what you want! No need to remember…

 

h/t to https://www.rubyguides.com/2018/10/rspec-mocks/ for showing me this.