MSpec 2.0 - I'm digging https://github.com/rubyspec/mspec/blob/80b78a81929a32c38410126561f5b9b8fc85a848/README.md

example.mspec.2.0.draft.rb

behavior :array_uniq_on_dupulicated_elements, :shared => true do
  it "returns a squashed array" do
    verify([1, 1].send(@method)).is.eq([1])
  end
end

describe "Array#uniq" do
  context "when elements are duplicated" do
    verify.behavior(:array_uniq_on_dupulicated_elements, :uniq)

    before(:each) do
      @array = [1, 1]
    end

    it "returns a new array" do
      ret = @array.uniq
      verify(ret).isnt(@array)
      verify(ret).is.instance_of(Array)
    end
  end
end

describe "Array#uniq!" do
  context "when elements are duplicated" do
    verify.behavior(:array_uniq_on_dupulicated_elements, :uniq!)

    before(:each) do
      @array = [1, 1]
    end

    it "returns self" do
      verify(@array.uniq!).is(@array)
    end
  end
end