Lets say we're going to apply 1 Watt of power to a speaker with a DC resistance of 8 Ohms.

According to a variation of the power formula:

V = square root (PR)

where

V is Voltage
P is power in Watts
R is DC resistance in Ohms

we have

V = square root (1 x 8)
V = 2.8 Volts

As another check let's say we apply a 9 Volt battery to an 8 Ohm speaker where:

P = V^2 / R

we have

P = 9^2 / 8
P = 10.125 Watts

Is 10 Watts too much? Personally, I wouldn't do it to a tweeter but I'm fine testing a woofer like that.

I would also make just a momentary connection, only enough to verify cone movement and then quickly disconnect.