Process like the litmus test ends (6)
I believe the answer is:
digest
'process' is the definition.
(digesting is a kind of processing)
'like the litmus test ends' is the wordplay.
'like' becomes 'dig' (I've seen this in other clues).
'ends' indicates one should take the final letters.
The final letters of 'the litmus test' are 'est'.
'dig'+'est'='DIGEST'
(Other definitions for digest that I've seen before include "Periodical that summarises the news" , "Shorten" , "Assimilate - summary" , "Absorb and assimilate, like food" , "Long walk, itinerant person" .)