There might be more than one method.
1.
Sweeping sine wave from lowest to highest frequency. Cater its sweep speed to the response time needed at each frequency of interest. That is to say, how many cycles it takes the network to let itself be instigated into resonant behavior at that frequency?
2.
One click (sudden change in voltage), may be sufficient to instigate all networks to ring (oscillate for a few cycles). Immediately after the click it could make a difference whether you connect the network to low impedance or high impedance, depending on topology.
3.
White noise at high amplitude. Supposedly it contains all frequencies, therefore all networks should respond (in theory). However it may depend on a networks Q figure, which is a clue to its amount of inertia.