One who won't give up being testy? (5)

I believe the answer is:

trier

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'one who won't give up being testy?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.

This is all the clue.

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(Other definitions for trier that I've seen before include "One persevering" , "conscientious type?" , "One always ready to have a go" , "One who makes an effort" , "place in Germany" .)

I've seen this clue in the Evening Standard.

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