Rails 5 Test Prescriptions

Using Mocks to Simulate Database Failure

A common use case for test doubles in Rails is to simulate database failures. Let’s look at how you might do that.

In the past, I would have suggested testing for failure at the controller level. However, Rails has basically deprecated controller tests for reasons I’ll talk about in Chapter 11, ​Testing Rails Display Elements​, and so I’d like to stay within the bounds of Rails community behavior.

Let’s look at the project-creation functionality you wrote at the beginning of the book. You wrote a controller:

mocks/01/app/controllers/projects_controller.rb

def create
  @workflow = CreatesProject.new(
    name: params[:project][:name],
    task_string: params[:project][:tasks])
 @workflow.create ...