mock_problems.rb

# common use of mocks in a Rails app
it "updates the requested book" do 
  mock_book = mock(:book)  
  Book.should_receive(:find).with("37").and_return(mock_book) 
  mock_book.should_receive(:update_attributes).with({:these => 'params'}) 
  put :update, :id => "37", :book => {:these => 'params'}
end

# without mocks a more readable, less brittle test
it "updates the requested book" do 
  a_book = Book.create(:author => 'an author') 
  put :update, :id => a_book.to_param, :book => {:author => 'JR Hartley'} 
  assert_equal 'JR Hartley', a_book.author
end