Anonymous police department experiment will conclusively tell you everything you need to know (8)

I believe the answer is:

acidtest

I'm a little stuck... Click here to teach me more about this clue!

'will conclusively tell you everything you need to know' is the definition.
I can't tell whether this defines the answer.

'anonymous police department experiment' is the wordplay.
'anonymous' becomes 'a' (this might be a standard abbreviation of which I'm unaware).
'police department' becomes 'CID' (abbreviation for Criminal Investigation Department).
'experiment' becomes 'test' (test is a kind of experiment).
'a'+'cid'+'test'='ACIDTEST'

Can you help me to learn more?

(Another definition for acidtest that I've seen is " It might provide proof".)

I've seen this clue in The Irish Times and the Irish Times (Crosaire).

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