When we manufacture certain PCBs, where 50ohms impedance matching is required the manufacturer provides a small PCB strip along with the actual PCB. What is the actual purpose of this?
To verify that the matched impedance is in fact 50 ohms.
You can use a network analyzer or Time domain reflectometer (TDR) to measure the impedance.
I'm not quite sure about this, but it might be possible to use a spectrum analyzer with build-in tracking generator to get an idea about the impedance. The phase information will be missing thou.