Exercise 1: A Third Order-Dependent Test — Possible Solution
====================================================================

THE THIRD TEST
------------------------------
    def test_third_order_is_order_number_one_too():
        result = process_order('C3', 90)
        return result['total_processed'] == 1

Added alongside the chapter's own two tests, sharing the same
module-level processed_orders list.

RESULTS (all 6 possible orderings of 3 tests)
------------------------------
    ('first', 'second', 'third'):  passing = ['first']
    ('first', 'third', 'second'):  passing = ['first']
    ('second', 'first', 'third'):  passing = ['second']
    ('second', 'third', 'first'):  passing = ['second']
    ('third', 'first', 'second'):  passing = ['third']
    ('third', 'second', 'first'):  passing = ['third']

In every one of the 6 orderings, exactly 1 of the 3 tests passes - and
it is always whichever test happened to run first.

WHY THIS WORKS AS AN ANSWER
------------------------------
This confirms the chapter's own finding generalizes beyond two tests:
the shared processed_orders list only ever equals length 1 immediately
after the very first append to it, ever, in the whole run. Since every
test's own assertion checks for exactly that condition, at most one
test can ever observe it - not because of anything special about which
test that is, but purely because only one test call in the whole
sequence can be the first one to touch the shared list.