Rails 5 Test Prescriptions

Mock Expectations

A mock object retains the basic idea of the stub—returning a specified value without actually calling a live method—and adds the requirement that the specified method must be called during the test. A mock is like a stub with attitude, expecting—nay, demanding—that its parameters be matched in the test or else you get a test failure.

In RSpec, you use the expect method to create mock expectations. This can be applied to full or partial doubles:

it "expects stuff" do
  mocky = double("Mock")
  expect(mocky).to receive(:name).and_return("Paul")
  expect(mocky).to receive(:weight).and_return(100)
  expect(mocky.name).to eq("Paul")
end

This test fails:

Failures:
  1) Project expects stuff
 Failure/Error: expect(mocky).to ...