Effective Testing with RSpec 3, Testing in Isolation: Unit Specs

Notes from Effective Testing with RSpec 3, chapter 5.

Martin Fowler’s article on Unit Tests defines them with the properties:

small scope, done by the programmer herself, and fast — mean that they can be run very frequently when programming.

Effective Testing & RSpec also take this philosophy. What differentiates Unit Tests from others is the degree of isolation. If the dependencies allow, we focus on just the class. Otherwise, we may need to focus on a set of classes for a specific behavior.

This is where Effect Testing has taken a left turn. With the majority of my projects being in a Rails context I think of Unit tests as the Model layer in a MVC framework. In this chapter, we practice Unit Tests at the request/controller layer.

Typically, you test a class through its public interface, and this one is no exception. The HTTP interface is the public interface.

Excerpt From: Myron Marston, Ian Dees. “Effective Testing with RSpec 3.”

I’m pretty stuck in my thinking of what a Unit Test is. This is helping me redefine it. They’ve linked to Xavier Shay who dares to toss the templated test directory and replace them with a different structure.

Unit Tests aren’t specifically for models but any object. Integration isn’t just for controllers but code operating against code that cannot change; usually helpers and presenters. Xavier tosses Functional in favor of Acceptance.

While different, this still feels natural. What category of test you want to run will depend on where you’re working in the codebase. This categorization of tests is another mental layer of filtering, which is important. It’s how we automate a necessary level of tests while still being efficient with test driven development.

We are advised to watch Gary Bernhardt’s talk on boundaries. I wanted to include it here because Gary provides a great example of how a difficult test demonstrates a refactoring opportunity in the codebase.

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.

Effective Testing with RSpec 3, The RSpec Way

Notes from Effective Testing with RSpec 3, chapter 3.

Benefits

Out of the half dozen listed benefits of TDD, I connected with two of them.

Enabling Refactoring/Create confidence

There have been moments where I completed a feature with 20-30 minutes left in the day. Enough time to clean up my code. This could lead to application failures surprising in scope or process. Scrambling to revert my changes I would end the day lost and confused. With tests already written, refactoring is a rewarding process. Having immediate failure in context teaches me where I am wrong about the application or technology.

Guiding Design

Writing tests get’s the abstract concepts out of our heads and into a concrete plan. It helps us recognize better design and separate ideas. Effective Testing points out that if writing specs for your current code base feels painful then it indicates the code is difficult to maintain and is an opportunity for refactoring.

Costs of a Test Suite

When a test suite is slow it translates into a monetary cost. If a developer is waiting 4 minutes for a tests suite to run there is an additional cost as that developer eases back into their workflow.

Tests that break easily or throw false positives are another time sink. It takes time and cognitive ability to understand the scope of the problem and how to resolve it.

An overdone test suite contains all of the above problems in addition to maintenance. Effective Testing quotes Kent Beck from stack overflow, I believe this is the quote I was thinking of from chapter 1,

I get paid for code that works, not for tests, so my philosophy is to test as little as possible to reach a given level of confidence…

A test creates a dependency on your codebase. If that bit of code is modified or removed you also have to update that test. Effect Testing recommends avoiding this dependency as best as you can. One way is to not tests code that frequently changes such as a user interface. Another way is to generalize your tests. Instead of looking for an ‘exact match’ check if the value is included.

Sandi Metz presents an additional view for writing tests. Separate tests from your public and private interface. We should only be concerned with the accessible parts of our classes. She keeps tests for private methods in a separate file. In a comment it instructs the reader to not fix failing tests but delete them. Private methods are meant to support the public. They are likely to change more frequently and drastically over their public siblings.

Types of Specs

RSpec supports many different types of tests but Effective Testing will focus on three.

Acceptance

End to end testing. I’ve written about acceptance testing before. It’s a great way to lay some ground coverage and start refactoring.

It’s not ideal for long term maintenance as it tends to be brittle and change frequently as an application changes.

Unit

Unit specs are tests that describe a class or methods behavior. These seem to be the most common type of test. It’s the fastest turn around time for writing a spec, failing it, making it succeed, and then refactoring.

These tests aren’t as useful for larger scopes of refactoring. They often describe your application in bite sized chucks but not a feature from end to end.

Integration

Integration specs sit in-between acceptance and unit. This is the code that interacts with external services and api’s. In Ruby on Rails projects we use integration tests to describe behavior at the controller layer.


The authors of Effective Testing have prepared us with the benefits and costs of testing. They have described three different types of tests with the benefits of each. With the basics of RSpec at hand we will spend Part 2 of the book diving deeper into Acceptance, Integration, and Unit testing.