rspec-set.rb

require 'rspec'

def set(attribute, &block)
  before(:all) do
    instance_variable_set("@#{attribute}", yield)
  end

  let(attribute) { instance_variable_get("@#{attribute}") }
end

class Foo
  attr_reader :bar

  def initialize(i = 0)
    @bar = i
  end

  def bar!
    @bar += 1
  end
end

describe :set do

  set(:foo)   { Foo.new }
  let(:foo2)  { Foo.new }
  set(:foo3)  { Foo.new(10) }

  it "should have foo.bar == 0" do
    foo.bar.should == 0
  end

  it "should have foo2.bar == 0" do
    foo2.bar.should == 0
  end

  it "should have foo3.bar == 10" do
    foo3.bar.should == 10
  end

  context "when incremented" do
    before(:all) do
      foo.bar!
      foo2.bar!
      foo3.bar!
    end

    it "should have foo.bar == 1" do
      foo.bar.should == 1
    end

    it "should have foo2.bar == 0" do
      foo2.bar.should == 1
    end

    it "should have foo3.bar == 11" do
      foo3.bar.should == 11
    end
  end
end