Measuring amperage with many flashlights is easy. For example-
Maglites- Pull endcap, turn switch to on, set multimeter to 2000ma, and then setting probes between exposed battery negative and non-anodized inner casing.
Nine volt lights can be checked by pulling the 9v clip on one side and inserting the meter probes between the now-exposed battery terminal and clip.
A little ingenuity will allow you to find somewhere to insert those probes into the circuit on most lights that I have worked with.