Karlotcha

#Model 

@user.should have(1).error_on(:username) # Checks whether there is an error in username 
@user.errors[:username].should include("can't be blank")  # check for the error message 

#Rendering
response.should render_template(:index)

#Redirecting 
response.should redirect_to(movies_path)

Karlotcha

# tail call optimization
RubyVM::InstructionSequence.compile_option = {:tailcall_optimization => true,:trace_instruction => false}

# Fibonacci sequence
def fib(n,tail,tail2)
  return 1 if n == 1
  return 1 if n == 2
  return tail + tail2 if n == 3
  fib(n-1, tail2, tail+tail2)
end