Test-Driven Development with Rspec

Objectives

Review the concepts behind TDD
Setup rspec for running tests in Ruby
Use a testing suite in the context of TDD

Test-Driven Development (TDD)

Test-driven development (TDD) is a software development process that relies on the repetition of a very short development cycle: first the developer writes an (initially failing) automated test case that defines a desired improvement or new function, then produces the minimum amount of code to pass that test, and finally refactors the new code to acceptable standards. - wiki

Process

Create / receive feature specification
Create test
Run tests (new test should fail)
Write code to try to make the test pass
Run tests (if fail return to step 4)
Refactor code if needed

How to get started

Rspec is the testing framework we are going to be using for Ruby (including Rails). To get started:

gem install rspec

(you might have to sudo this depending on your machine settings)

Once you have successfully installed rspec, create a new project:

rspec --init 
# (this will create a .rspec and spec/spec_helper.rb file)

Inside your .rspec file make sure you have this text

--color
--require spec_helper
--format documentation

Requiring files

require

This will load a ruby file ONCE and only once. All subsequent require statements will not reload the file.
Doesn't need the .rb file extension, but won't hurt if it's there.

require_relative

Same as require, but will look for the file to require in the same directory

Rspec matchers

expect(actual).to be ___
expect(actual).to be_between(minimum, maximum).inclusive
expect(actual).to match(/expression/) # We will learn about this very soon!
expect(actual).to be true      # passes if actual == true
expect(actual).to be false     # passes if actual == false
expect(actual).to be_nil       # passes if actual is nil
expect(actual).to be_instance_of(Class)       # passes if actual is an instance of a certain Class
expect(actual).to exist        # passes if actual.exist? and/or actual.exists? are truthy

The rspec documentation is a great place to find more of these - you can find them here

Writing your first test

Create a new file in the spec folder ending with _spec. In this example, we'll name our first test tests_spec.rb

Start with requiring spec_helper, then add a describe block, and inside an it statement as well

require 'spec_helper'

describe "Some idea, variable or method" do
  it "is something or does something" do
    # expect...
  end
end

Let's start with some very simple tests

describe "Random Tests" do
  it "should result in 5 equaling 5" do
    expect(5).to eq(5)
  end

  it "should result in 5 not equaling 3" do
    expect(5).to eq(3)
  end

  it "does something that is pending", pending: true do
    expect(5).to be < 3
  end

  xit "does something that is pending because we used xit" do
    expect(5).to be < 3 #this will be pending
  end
end

for more information see the RSpec documentation

I'm getting errors!

Make sure you have done rspec --init so that you have a .rspec file and a spec folder with a spec_helper.rb file
Did you mean to do require_relative instead of require?
If you do use require_relative, make sure you have the exact path

Hooks

RSpec also supports before and after hooks which can be triggered before or after each example or once for the entire context (all things in a describe block). This is useful for doing things like initializing an instance of a class before testing it.

Here is a basic example using before

describe Item do

  before(:context) do
    @item = Item.new("Generic Item",1.99)
  end

  describe "Initialization" do
    it "is an instance of the Item class" do
      expect(@item).to be_instance_of(Item)
    end
  end
end

More details hooks in RSpec docs

Ruby Testing with Rspec