Feel it must break up test material (6)
I believe the answer is:
litmus
'up test material' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'feel it must break' is the wordplay.
'LITMUS' is hidden in amongst the letters.
However, I am uncertain how this is indicated.
Can you help me to learn more?
(Other definitions for litmus that I've seen before include "Old dance" , "Substance used in test for acidity" , "Paper used to test for acid or alkali" , "Colouring material used as a rough acid-base indicator" , "Substance used to tell acid from alkali" .)