Test::mocktime::datecalc arranges for the functions in date::calc to follow the perl level 'time' function, and in particular any fake date/time set there by test::mocktime. the following date::calc functions are changed

system_clock
today
now
today_and_now
this_year
gmtime
localtime
timezone
time_to_date
gmtime, localtime, timezone and time_to_date are made to default to the perl-level current time. when called with an explicit time argument they're unchanged.