Solution
NI DMMs use a current source for resistance measurements, this current is forced through the leads and then the voltage generated by the resistance is read by the DMM to calculate that resistance using Ohm's Law, as is shown in the image below.
The Max Test Voltage mentioned in the specifications of NI DMMs (see table below), refers to the maximum voltage that the DMM can measure in a specific range, before returning an Over Range status. In other words, the Max Test Voltage tells you what is the voltage at maximum resistance that can be measured with a specific range.
For example, the table above is from the NI-4080, if you select the 100 ohms range, the Max Test Voltage is 100 mV, with a current of 1 mA this means that the maximum resistance value that the DMM can measure on that range is 100 ohms, anything above that will return an Over Range status.
Note: The Max Test Voltage is not the compliance voltage of the DMM, the DMM might go above the Max Test Voltage depending on the resistance that is trying to be measured.