Suppose you want a subroutine to do a task by splitting it into smaller subroutines. Testing the bigger subroutine becomes increasingly difficult, specially if you cannot ensure that the smaller subroutine is correct.

An embedded TS subroutine could allow to emulate, in a higher level language (TS), the results of the subroutine so that when testing the larger subroutine you can be sure that no smaller subroutines are failing.

NOTE: This only works as long as your higher level code isn't wrong.