[perl #38982] [TODO] refactor long test files

[Jerry Gay]

# New Ticket Created by jerry gay
# Please include the string: [perl #38982]
# in the subject line of all future correspondence about this issue.
# <URL: https://rt.perl.org/rt3/Ticket/Display.html?id=38982 >

some test files are too long to be maintainable. for example,
t/op/calling.t is ~2400 lines. this, and other files like it, should
be split into smaller files.

there's a lot of room here for judgement.
try to keep similar tests together.
try to keep the files under, say, 1000 lines.
the rest is up to you.

~jerry