"Testing criteria", i.e. determining what you are testing for, is made during testing.
No, you don't have to make
any assumptions at all.
The study design is quite explicit in it's description of the problem solving methodology. Page 17 of the study design refers to your question.
Testing whether the solution does what it was intended to do. This activity typically involves:
− establishing what tests will be conducted
− determining what test data, if any, will be used
− determining expected results
− conducting the test
− recording the actual results
− correcting any identified error
Anything about the problem solving methodology that isn't in the document isn't in the study design. If your definition of testing criteria is different to determining what you are testing for, then it's not on the study design.
edit: I'm pretty sure we're talking about the same thing here