Hampshire river flow trial (4,3)

I believe the answer is:

test run

'trial' is the definition.
(I've seen this before)

'hampshire river flow' is the wordplay.
'hampshire river' becomes 'test' (River Test).
'flow' becomes 'run' (run is a kind of flow).
'test'+'run'='TEST-RUN'

(Another definition for test run that I've seen is " Trial performance".)

I've seen this clue in The Times.

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