University dons joke before English test (5)
I believe the answer is:
gauge
'test' is the definition.
(thesaurus)
'university dons joke before english' is the wordplay.
'university' becomes 'u'.
'dons' is an insertion indicator (don means to wear or put on).
'joke' becomes 'gag' (synonyms).
'before' means one lot of letters go next to another.
'english' becomes 'e' (abbreviation).
'u' put inside 'gag' is 'gaug'.
'gaug'+'e'='GAUGE'
(Other definitions for gauge that I've seen before include "Judge" , "Measure against a standard" , "Estimate, form judgement of" , "standard size" , "Rail track width" .)