Why does the exitstatus parameter in the pytest_terminal_summary hook function return the number 0 when the test passes and an enumerated value in other cases?

[backtracker]

#: Tests passed.
OK = 0
#: Tests failed.
TESTS_FAILED = 1
#: pytest was interrupted.
INTERRUPTED = 2
#: An internal error got in the way.
INTERNAL_ERROR = 3
#: pytest was misused.
USAGE_ERROR = 4
#: pytest couldn't find tests.
NO_TESTS_COLLECTED = 5

[RonnyPfannschmidt]

Programm return codes indicate errors in general

0 means no error