Sure, here are some postconditions for ChangeOil():

- engine has appropriate amount of oil in it

- oil filter in place

- drain plug torqued correctly

- dip stick present

- oil cap on

No matter what the outcome of the operation (ie error paths or happy path), ChangeOil promises to return with the car in a state that fulfills those conditions.

In order to do that, some preconditions need to be fulfilled too:

- car has some amount if oil in engine

- car is able to start

- no major noises

Yes and frame conditions… Wheels should still where they were, nothing stolen from the glovebox, no bodies added to the trunk, brake lines uncut, etc.

For instance, does the old oil need to be drained before filling new oil?

Does the car need to be checked for leaks?

At the end of filling in new oil, how much oil should be in the car? How much left over?