Tested guided missile power at first (7)

I believe the answer is:

sampled

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

'tested' is the definition.
Although both the answer and definition are past participle verbs, I can't understand how they can define each other.

'guided missile power at first' is the wordplay.
'guided' becomes 'led' ('lead' can be a synonym of 'guide').
'missile' becomes 'sam' (SAM is an example).
'power' becomes 'p'.
'at first' means one lot of letters go next to another.
'sam'+'p'='samp'
'led' after 'samp' is 'SAMPLED'.

Can you help me to learn more?

(Other definitions for sampled that I've seen before include "Tasted" , "tried" .)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.