Effective Testing with RSpec 3, Starting On the Outside: Acceptance Specs

Notes from Effective Testing with RSpec 3, chapter 4.

In this chapter we start by building our application guided by tests. This seemed extreme for me. Normally, I would setup the required dependencies; install libraries, setup database, and initiate the application.

Effective Testing does everything through the test file. Our first file is a test to ensure we can post an expense. It doesn’t even contain any expectations, it just assumes we have an api and we can perform a post (we do not). We then start running tests and build the dependencies based on failures.

Here’s a TDD example of vacuuming the rug.

  1. start vacuum
  2. FAIL – there is no vacuum
  3. buy vacuum
  4. FAIL – cannot find vacuum
  5. put vacuum in the closet

This goes on and on until we have an api mocked and ready to go. Throughout the chapter the focus is always on the tests. In ‘Filling In the Response Body’ we go as far as to put a hard coded response in our api. No matter what we post we will always receive { “expense_id”: 42 }. We continue to build out a test suit on this hard coded response.

Top Down Testing

There are a few names for this philosophy of testing; Top-Down, Outside-In, Discovery, or London style. The idea is that we start with the purpose of the application and work down to the details. This is accomplished by mimicking the response we’re looking for as we’ve done with { “expense_id”: 42 }.

Justin Searls, vocal proponent for Top Down has written about the benefits and provides a youtube series of it in action.

The appeal to this style of testing is that it naturally flows with our train of thought. We know the purpose, what components we need to serve that purpose, and how those components act. The perceived bottle neck with TDD is that we stay in the details too long and forget how those details talk to each other.

Top down has it’s own criticisms. It’s mock heavy which can lead to false positives, create a test suite full of objects that don’t exist, and some consider mocking a code smell.

I’m expecting that Effective Testing will address these criticisms and provide solutions to avoid them.

Notes & Observations

Effective testing instructs us to use bundle exec rspec. I prefer binstubs for the tab-complete goodness. You can generate one with bundle binstubs rspec-core from your projects root directory. Then run rspec with bin/rspec.

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