To fool the testers, the earth ground terminal is shorted to the neutral at the post!
You may be correct but I am not absolutely sure. I think a good tester would know if the neutral was common at the outlet otherwise any and all circuits in any house could fool the electrical inspector in the USA when he walks through the house randomly checking outlets with the same tester we would use - I have seen this done and they don't open outlets to physically check the outlet - they use a tester. I think there has to be a specific ground wire going from the main panel to any and all outlets. I think in Mexico there are people who will tie the ground slot of the outlet to the neutral wire but I don't think this would fool a tester - otherwise testers would be pointless anywhere. Testers are designed to recognize cheaters. But I am not 100% certain.