Developer test codes

Are there any developer test codes or field test codes ? I want to purchase used mate 7 and i always run field test before purchasing used phones. i tried google search and xda search but couldn't find anything useful. thanks for your time

Hidden menu codes? 6045I

Was wondering if anyone knew dialer codes for this phone? In particular I'm trying to try and force Band 4. At home my phone keeps jumping back and forth between band 4 and 12 and band 4 is much faster .

Thanks