Test taken by a swimmer around the end of May (3-3)

I believe the answer is:

try-out

'test' is the definition.
(try out can mean to test or trial)

'a swimmer around the end of may' is the wordplay.
'a swimmer' becomes 'trout' (trout is a kind of aquatic vertebrate).
'around' indicates putting letters inside.
'the end of' suggests the final letters.
The last letter of 'may' is 'y'.
'trout' placed around 'y' is 'TRY-OUT'.

'taken by' is the link.

(Another definition for try-out that I've seen is " Test performance".)

I've seen this clue in the Evening Standard.

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