maybe turn on the light, stick it in a glass of water, and then freeze the water. It would look impressive, but I'm not sure how likely it might be to damage the light. Might crack the lens??
for more realistic tests, vibration testing and thermal cycling are pretty standard. Thermal shock is common too. Might even go for a chemical resistance test (i.e. how does it survive exposure to the various chemicals that it may be exposed to. This might be limited to diet coke, coffee, maple syrup, and salsa, in some cases).
An endurance test of the switch might be useful too. This is a little tougher to set up.
For reference, I'm involved with electronics development for construction equipment, and previously designed 'tronics for military aircraft and spacecraft, so I've seen some pretty tough tests.
Steve K.