Willing to put everything one has under tension (7)

I believe the answer is:

testate

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

I can't explain the rest of the clue.

(Other definitions for testate that I've seen before include "Dying with a will" , "With a legally valid will" , "Having left a legacy" , "State of having made a will" , "Having written a valid will" .)

I've seen this clue in The Guardian.

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