The most common and most likely answer to this crossword clue is the 6 letter word CANOPY
I've seen this crossword clue in The Guardian
C
A
N
O
P
Y
More clues leading to the result CANOPY
- Cover model going round Angola
- Tester needs one to probe ape
- An ape crosses the treetops
- Shade article put into forge
- Cover what journalists write about article
- Sky put article in text of news story
- Ape gathers one in the treetops
- Image over an awning
- Covering article smuggled aboard by pirate
- Run off to fix an awning
Buddy explains!

The straight part
We know that "Tester" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tester = canopy.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CANOPY mean?
CANOPY noun- A high cover providing shelter, such as a cloth supported above an object, particularly over a bed.
- Any overhanging or projecting roof structure, typically over entrances or doors.
- The zone of the highest foliage and branches of a forest.
- In an airplane, the transparent cockpit cover.
- In a parachute, the cloth that fills with air and thus limits the falling speed.
- To cover with or as if with a canopy.
- To go through the canopy of a forest on a zipline.