Pupil eager to take test with thug, oddly (3,7)
I believe the answer is:
art student
'pupil' is the definition.
(art student is a kind of pupil)
'eager to take test with thug oddly' is the wordplay.
'eager' becomes 'ardent' ('ardent' can be a synonym of 'eager').
'to take' means one lot of letters goes inside another.
'test with' becomes 'ts' (I can't justify this - if you can you should give a lot more credence to this answer).
'oddly' means one should take alternating letters.
The alternating letters of 'thug' are 'tu'.
'ts'+'tu'='tstu'
'ardent' enclosing 'tstu' is 'ART STUDENT'.
(Another definition for art student that I've seen is " Someone learning to paint".)