What are the limitation of unit testing?

• Unit test can only show the presence of the errors, It cannot show absence of the errors.It only test the functionality of the each module separately.                                                                             
• Unit tests don't check the integration between each module.Therefore it will not find integration errors broader system level errors.                                                                                         
• When a major function of the method is to interact with something external to the application, It is not easy to create test cases. ex:a method that work with database.