Williamseal, both those clues split in two.
20 The first half is the fish (reversed as the clue says 'return') and a three letter word (abbreviation/acronym) for 'test'.
15. The first half equals 'locks' - if you've the last three letters, you should see what kind of 'locks', ie not for doors. The second half is defined in Chambers as a 'route or course taken by someone...' If you've completed the grid, the word will be there already.