First of all, do they all have to be tested during the same class? If not, focus on testing a few students in each lesson. Depending on the size of the class and discipline issues, you could also set students a task to do in groups. Go around spending some time with each group; that may help you get around all the students more quickly.
As for what you test, I would suggest focussing on the sounds that the Chinese generally find difficult to produce. This might be the distinction between “l” and “r”. Make a list of sounds that are difficult for them and you could give them a mark for getting one right. Remember to grade intonation and stress (including unstressed sounds or the schwa). Remember as well to give a mark for overall intelligibility. You could grade them out of ten, giving two marks for overall intelligibility, 2 marks for stress, 2 marks for intonation and 4 marks for sounds that you have identified as being difficult. Think carefully about how you would do it because it could become cumbersome. In any case, it is not a good idea to ask students to read something and to grade their pronunciation; pronunciation almost always sounds worse when reading aloud.
As for different accents (UK, US, NZ etc), that shouldn’t be an issue; you can mark everything as being right no matter what accent the students use.
All the best,