Blog Code: Drying Out Specs with Shared Examples

0_simple_class_spec.rb

require "spec_helper"
 
describe SimpleClass do
 
  before do
    subject.name = "Some Name"
    subject.description = "Some Description"
  end
 
  its(:name) { should eq("Some Name") }
  its(:description) { should eq("Some Description") }
end

1_simple_class.rb

class SimpleClass
  attr_accessor :name, :description
end

2_simple_class_spec.rb

require "spec_helper"
 
describe SimpleClass do
 
  before do
    subject.name = "Some Name"
    subject.description = "Some Description"
  end
 
  its(:name) { should eq("Some Name") }
  its(:description) { should eq("Some Description") }
 
  describe "#name" do
 
    context "when not supplied" do
      before do
        subject.name = ""
        subject.valid?
      end
 
      it { should_not be_valid }
 
      it "should have an error" do
        expect(subject.errors.size).to eq(1)
        expect(subject.errors[:name]).to_not be_nil
      end
    end
  end
 
  describe "#description" do
 
    context "when not supplied" do
      before do
        subject.description = ""
        subject.valid?
      end
 
      it { should_not be_valid }
 
      it "should have an error" do
        expect(subject.errors.size).to eq(1)
        expect(subject.errors[:description]).to_not be_nil
      end
    end
  end
end

3_gemfile

# you can omit the version if you don't need it
gem "activemodel", "~> 4.0.0"

4_simple_class.rb

require "active_model"
 
class SimpleClass
  include ::ActiveModel::Validations
 
  attr_accessor :name, :description
 
  validates_presence_of :name, :description
end

5_simple_class_spec.rb

require "spec_helper"
 
describe SimpleClass do
 
  before do
    subject.name = "Some Name"
    subject.description = "Some Description"
  end
 
  its(:name) { should eq("Some Name") }
  its(:description) { should eq("Some Description") }
 
  shared_examples_for "a required property" do
    # requires that "field" be defined
    before do
      subject.__send__("#{field}=", "")
      subject.valid?
    end
 
    it { should_not be_valid }
 
    it "should have an error" do
      expect(subject.errors.size).to eq(1)
      expect(subject.errors[field]).to_not be_nil
    end
  end
 
  describe "#name" do
 
    context "when not supplied" do
      let(:field) { :name }
      it_should_behave_like "a required property"
    end
  end
 
  describe "#description" do
 
    context "when not supplied" do
      let(:field) { :description }
      it_should_behave_like "a required property"
    end
  end
end