I'm not sure that it's novel but I'm skeptical about the noise to signal ratio for anything that is not an example.

I think that a real world file of source code will be either completely polluted by tests (they are way longer than the actual code they test) or become

  fn process_order {
    ... 
  } 
  shadow process_order {
    assert test_process_order
  }

and the test code will be written in another file, and every function in the test code will have its own shadow function asserting true, to please the compiler.