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Project: RSpec Core 2.6

Publisher: RSpec

shared examples

Shared examples let you describe behaviour of types or modules. When
declared, a shared group's content is stored. It is only realized in the
context of another example group, which provides any context the shared group
needs to run.

A shared group is included in another group using any of:

include_examples "name"      # include the examples in the current context

it_behaves_like "name"       # include the examples in a nested context
it_should_behave_like "name" # include the examples in a nested context
Scenarios
  1. shared examples group included in two groups
  2. Providing context to a shared group using a block
  3. Passing parameters to a shared example group
  4. Aliasing "it_should_behave_like" to "it_has_behavior"
shared examples group included in two groups
Given
a file named "collection_spec.rb" with: 
require "set"

shared_examples "a collection" do
  let(:collection) { described_class.new([7, 2, 4]) }

  context "initialized with 3 items" do
    it "says it has three items" do
      collection.size.should eq(3)
    end
  end

  describe "#include?" do
    context "with an an item that is in the collection" do
      it "returns true" do
        collection.include?(7).should be_true
      end
    end

    context "with an an item that is not in the collection" do
      it "returns false" do
        collection.include?(9).should be_false
      end
    end
  end
end

describe Array do
  it_behaves_like "a collection"
end

describe Set do
  it_behaves_like "a collection"
end
When
I run rspec collection_spec.rb --format documentation
Then
the examples should all pass
And
the output should contain: 
Array
  behaves like a collection
    initialized with 3 items
      says it has three items
    #include?
      with an an item that is in the collection
        returns true
      with an an item that is not in the collection
        returns false

Set
  behaves like a collection
    initialized with 3 items
      says it has three items
    #include?
      with an an item that is in the collection
        returns true
      with an an item that is not in the collection
        returns false
Providing context to a shared group using a block
Given
a file named "shared_example_group_spec.rb" with: 
require "set"

shared_examples "a collection object" do
  describe "<<" do
    it "adds objects to the end of the collection" do
      collection << 1
      collection << 2
      collection.to_a.should eq([1,2])
    end
  end
end

describe Array do
  it_behaves_like "a collection object" do
    let(:collection) { Array.new }
  end
end

describe Set do
  it_behaves_like "a collection object" do
    let(:collection) { Set.new }
  end
end
When
I run rspec shared_example_group_spec.rb --format documentation
Then
the examples should all pass
And
the output should contain: 
Array
  behaves like a collection object
    <<
      adds objects to the end of the collection

Set
  behaves like a collection object
    <<
      adds objects to the end of the collection
Passing parameters to a shared example group
Given
a file named "shared_example_group_params_spec.rb" with: 
shared_examples "a measurable object" do |measurement, measurement_methods|
  measurement_methods.each do |measurement_method|
    it "should return #{measurement} from ##{measurement_method}" do
      subject.send(measurement_method).should == measurement
    end
  end
end

describe Array, "with 3 items" do
  subject { [1, 2, 3] }
  it_should_behave_like "a measurable object", 3, [:size, :length]
end

describe String, "of 6 characters" do
  subject { "FooBar" }
  it_should_behave_like "a measurable object", 6, [:size, :length]
end
When
I run rspec shared_example_group_params_spec.rb --format documentation
Then
the examples should all pass
And
the output should contain: 
Array with 3 items
  it should behave like a measurable object
    should return 3 from #size
    should return 3 from #length

String of 6 characters
  it should behave like a measurable object
    should return 6 from #size
    should return 6 from #length
Aliasing "it_should_behave_like" to "it_has_behavior"
Given
a file named "shared_example_group_spec.rb" with: 
RSpec.configure do |c|
  c.alias_it_should_behave_like_to :it_has_behavior, 'has behavior:'
end

shared_examples 'sortability' do
  it 'responds to <=>' do
    sortable.should respond_to(:<=>)
  end
end

describe String do
  it_has_behavior 'sortability' do
    let(:sortable) { 'sample string' }
  end
end
When
I run rspec shared_example_group_spec.rb --format documentation
Then
the examples should all pass
And
the output should contain: 
String
  has behavior: sortability
    responds to <=>

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