Given the fact that the four horsemen were so surprised when the chip tested positive, even though the bad guys all along believed them to have it, I find it highly unlikely that they built a false 'chip test device'. 

   I agree partially with user40779 however I believe it was probably the man (I can't recall his name) that was overlooking the chip when the horsemen originally stole it. He was revealed to me a member of the eye at the end of the movie and could have easily stolen it before the horsemen arrived having prior knowledge of their plan from what the grandmother in the magic shop overheard of Atlas's phone conversation. Supposedly all for the purpose of preventing it from falling into the wrong hands. From that point he handed it over to li and his grandmother for them to switch it with the fake and precede to the main event.

 At least that's the best I can come up with.

Given the fact that the four horsemen were so surprised when the chip tested positive, even though the bad guys all along believed them to have it, I find it highly unlikely that they built a false 'chip test device'.

I agree partially with user40779 however I believe it was probably the man (I can't recall his name) that was overlooking the chip when the horsemen originally stole it. He was revealed to me a member of the eye at the end of the movie and could have easily stolen it before the horsemen arrived having prior knowledge of their plan from what the grandmother in the magic shop overheard of Atlas's phone conversation. Supposedly all for the purpose of preventing it from falling into the wrong hands. From that point he handed it over to li and his grandmother for them to switch it with the fake and precede to the main event.

At least that's the best I can come up with.