customer_spec.rb

describe Customer, "last billing address" do
  before do
    @customer = Customer.generate!  
    @customer = Address.new
  end
  it "should be settable and gettable" do
    @customer.last_billing_address = @account_address
    @customer.last_billing_address.should == @account_address
  end  
  ...  
end

describe Customer, "last delivery address" do
  before do
    @customer = Customer.generate!  
    @account_address = Address.new
  end
  it "should be settable and gettable" do
    @customer.last_delivery_address = @account_address
    @customer.last_delivery_address.should == @account_address
  end
end

improved_spec.rb

share_examples_for "named address" do

  it "should be settable and gettable" do
    named_address = @account_address
    @named_address.should == @account_address
  end  
end  

describe Customer, "last billing address" do 
  it_should_behave_like "named address"

  before do
    named_address = @customer.last_billing_address=
    @named_address = @customer.last_billing_address