How do I execute an automated test with the option of specifying it as a unit test or integration test

How do I execute an automated test with the option of specifying it as a unit test or integration test without writing the same test twice and only changing the interface?

Specifically, I want to execute one test and specify it as a unit test or an integration test. Based on the mode I select, the test should generate a service interface that will

• I do not want to maintain two sets of identical code with the only difference being an interface:
  
  
  
  • Service for accessing external system (integration test)
  
  
  • MockService (unit test)