Take ADXL322 as example, the non-linearity spec is +/-0.2% of FS, how we run the measurement? is there a simple setup for the spec?
You will need a way of imparting different g-level (-2g to +2g for ADXL322) and recording the sensor output. We typically use a shaker table and generate g-forces at 20Hz. The slope of sensor output vs. input then shows the level of non-linearity.