In a group, nine out of twelve get a test - does Jack? (9)

I believe the answer is:

vegetates

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'does jack?' is the definition.
Although both the answer and definition are verbs in their -s form, I don't see how one could define the other.

'in a group nine out of twelve get a test' is the wordplay.
'VEGETATES' is hidden within the letters.
However, I am not sure how this is indicated.

Can you help me to learn more?

I've seen this clue in The Independent.

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