The physics behind humidity testing is analogous to temperature testing. Temperature testing reveals infant mortalities related to stresses that arise from the coefficient of thermal expansion of different materials. Humidity testing reveals infant mortalities related to stresses that arise from the coefficient of moisture expansion of different materials. Humidity testing can also reveal other nasties like contamination of solder joints, pins and interconnects and the PCB itself.
Humidity testing would be a good stressor for revealing the robustness of adhesives used in drivers.
