For these cases, you have to examine the whole of those friends' character. If that friend repeatedly brings up the same arguments 'just to test or practice', a

For these cases, you have to examine the whole of those friends' character. If that friend repeatedly brings up the same arguments 'just to test or practice', and/or if they reveal the fruits of those arguments in other aspects of their character or thought, you can make the argument to them that you cannot in good faith believe that they are merely holding that position for argument's sake. However, if they have a known position and they make arguments clearly outside those boundaries, and then /show that they return to their usual position after/, it is much more feasible to believe that they are indeed merely testing their own position thoroughly, as any reasoning person should.