Assume it's a fit test (3,2)

I believe the answer is:

try on

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'test' is the definition.
(try-on is a kind of test)

I cannot understand how the remainder of the clue works.

(Other definitions for try on that I've seen before include "Test a garment's size and look" , "attempted deception" , "attempt to deceive" , "Attempt at deception" , "Fitting" .)

I've seen this clue in the Evening Standard.

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