gistfile1.rb

class ExpensiveOperation
   def self.lookup(question)
      "This goes to the database"
   end
end

class UsesExpensiveOperation
   def initialize 
      @cache = {}
   end
   
   def answer_for(question)
      # oops, this is broken, it was supposed to be cached 
      # @cache[question] ||= ExpensiveOperation.lookup(question)
      @cache[question] = ExpensiveOperation.lookup(question)
   end
end

describe "suprising behavior" do
   before do
      @object = UsesExpensiveOperation.new
      
      ExpensiveOperation.stub(:lookup).and_return('whatever')
   end
   
   it "should fail because I'm specifying that lookup should be called at most one time, but that's not true" do
      ExpensiveOperation.should_receive(:lookup).at_most(:once).and_return('an answer')
      
      @object.answer_for("my question")
      @object.answer_for("my question")
   end

end