Emulating a Doppler Test under laboratory enviroments
It depends on exactly what parameters of the signal the receiver is interested in.

Doppler shift changes the frequency of all signals, carrier frequency, data rates, modulation offsets etc, by the same ratio.

Generally, as the carrier frequency is orders of magnitude above the data rate, it suffices to tune the signal generator to a different carrier frequency, and leave the data modulation alone, as the absolute shift at those lower frequencies will be negligible.

If the data rates are very high (for instance Ultra WideBand), or the carrier very low, or the Doppler shift very extreme, then you may need to shift the modulation generator parameters as well.

Some signal generators intended for communications test have Doppler capability built in, usually with fading models as well.