RSpec Explained

describe

    describe Cookie do
    end

• defines a context
• takes a class or a string as its name

it

describe Cookie do
  it "tastes yummy" do
  end
end

• defines an example
  • (aka spec or test)
• takes a string as its name

should

describe Cookie do
  it "tastes yummy" do
    cookie = Cookie.new
    cookie.chips.should == 72
  end
end

• defines an assertion
• every test needs at least one assertion
  • or else you're not really testing anything

matchers

describe Cookie do
  it "has approximately 70 chips" do
    cookie = Cookie.new
    cookie.chips.should be_within(5).of(70)
  end
end

• weirdo argument to should
• performs a test on the object that should is called on
• see http://rubydoc.info/gems/rspec-expectations#Built-in_matchers

be matchers

[].should be_empty

• uses method_missing magic
• be_empty invokes empty? on its target
• be_valid invokes valid? on its target
• and so on

before and after

describe Counter do
  before do
    @data = [0,1,2,3]
  end
  it "counts data" do
    Counter.new(@data).count.should == 4
  end
  it "adds data too" do
    Counter.new(@data).sum.should == 6
  end
end

• before blocks will be executed before each of the specs in that describe block
• there's also before :all do..end which executes only once
• there's also after with similar semantics

let

describe Counter do

  let(:data) { [0,1,2,3] }

  it "counts data" do
    Counter.new(data).count.should == 4
  end
  it "adds data too" do
    Counter.new(data).sum.should == 6
  end
end

subject

describe Counter do
  let(:data) { [0,1,2,3] }

  subject { Counter.new(data) }

  it { should be_a(Counter) }

  it { should_not be_nil }

  it "counts data" do
    subject.count.should == 4
  end

  it "adds data"do
    subject.sum.should == 6
  end

end

more

• Intro to RSpec Video from RailsConf 2012 on YouTube.
• BDD and Acceptance Testing with RSpec & Capybara Video from RailsConf 2013 on YouTube.
• Code School's RSpec Introduction Course

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