As has been pointed out - the time a test will remain positive for depends on how regularly cannabis is used.
A one off use, will likely be undetectable after 48-72 hours from last use.
If used regularly (2x a week) then because THC builds up in fat cells, this may increase to 96 hours.
If used every day for a prolonged period it can take up to 14 days for all the THC to wash out.
In extreme heavy use, this may take up to 21-28 days.