Recently I came across internet about SpaceX's Booster 7 explosion in a ball of fire during an engine spin up test. I searched Google about rocket engine spin up test but I got no hit. What is a rocket spin up test and how it differs from tests like static fire, pre-burner test?
During the spin up test, the fuel passes through the engine systems, but is not ignited in the gas generators. Instead of hot gases, the turbine spins cold gas supplied from the outside. It spins the turbine up to operating speeds, and the pumps pump fuel at norminal pressure. Roughly speaking, this is a spill test without ignition.