I spent some time at the Solihull plant before the previous Defender was retired. All models went through the water test, which included a deep dip and a trundle through a tunnel that did a pressure wash from all sides. For the Range Rovers and Discovery, no water was allowed inside. For the Defender, it was a pass provided you stayed dry above the knees.No need to have that spec in a Brit built Lanny. In every Defender/110 I've owned in the last 40 years; both footwells have leaked like buggary so the interior is always getting a nice wash/hose down.
After the water test, there was a concrete ramp that they had to park on for a few seconds. I initially thought it was a handbrake test. It was to let the water back out.