Think like the testmaker?

4 is fine. Reversing the verb and subject is acceptable.
2 and 5 are incorrect. You should not use a clause with "like" and a noun with "as".

Simple rule that you can follow for 'Like' vs 'As'

For the comparison of nouns/pronouns, use like

If you are comparing actions, use as. 'As' is even used for ROLE PLAY.

1. Think Like the testmaker. here "like" is followed with a noun.
2. Think as the testmaker. incorrect because as is used for comparing actions.
3. Think as the testmaker does. here as is used for the action that is 'testmaker's thinking'
4. Think as does the testmaker. here also same as 3.
5. Think like the testmaker does. here "like" is used for action so incorrect.

Also for 3 and 4, Reversing the verb and subject is acceptable in GMAT.

I can't see (4) ever being used in a correct answer on the GMAT in that form. Usually, if the subject and verb are reversed in a comparison, the meaning is different. It's not a straightforward comparison; instead, it means something like 'and the testmaker does the same thing.'

'Think, as does the testmaker' = the testmaker thinks, and you should think too. We could either think the same way, or differently, as long as we both think.
'Think as the testmaker does' = you should think in specifically the same way the testmaker thinks.

'I like to bake cookies, as does Laura' = Laura likes to bake cookies, and so do I. We could both bake cookies differently, or we could do it in the same way.
'I like to bake cookies as Laura does' = I like to bake cookies in exactly the same way (i.e. using the same ingredients, the same recipe, etc.) as Laura.

Thanks for clearing my mis-conception ccooley.

Check this post on my blog:
https://anaprep.com/sentence-like-vs-as/

It discusses "like" vs "as" usage.