I have been told that back when it was legal, some foxes will twist and turn with the best of them, hug the hedgerows, not come to a call and generally be very hard to pin down.........other times they will sprint in to their death, 4 yds and its all over.
Some would make a fight of it and others would be put away quickly and easily.
No different from any other wild animal really...........
Are they a test for a dog?, yes, sometimes they are..........but not always
Are they a test for the hunter?,.........just as above