How are in practice input output impedance measured of a prototype circuit?
For measuring output impedance, one invariably measures the output level while changing the load on the output.

For measuring the input impedance, a common technique is to use a controllable output impedance to drive the device, usually a voltage source with a series resistor, and monitor the output while the resistor is varied.

For 50 &Omega; RF devices, a network analyser is often used to measure S11 and S22.

For other devices, the variety of frequencies, waveforms, loads, voltages, means that any instrument dedicated to this task would be uneconomic, either addressing a very small section of the market, or having to be hopelessly comprehensive.