How to check if two device has the same address on I2C? I start a new project with Arduino UNO and MCP23017 expander. Using this, I can connect 8 chips on Arduino, by selecting different addresses ( from 0x20 to 0x27 ). 
My question is, if I connect two MCP23017 chips with the same address, there is any way to see somehow that I have two chips with the same address ?
I am using a standard I2C scanner in Arduino code, but is nt return me if I have multiple chips with the same address, he see only one chip for example !

Can you please help me with some ideas to check how man chips are connected with the same address?
It's my understanding that duplicate I2C addresses prevent the master from communicating from the slaved devices, so the answer is no.

Instead, connect the devices one at a time, run the I2C scanner, note the address for each, and take note of any duplicate addresses.