“An engine nozzle turns a dramatic array of colors during a recent hot-fire test at NASA's White Sands Test Facility near Las Cruces, N.M. A team of engineers from Glenn Research Center in Cleveland, Ohio, Marshall Space Flight Center in Huntsville, Ala., and Johnson Space Center in Houston conducted tests on a cryogenic liquid oxygen and liquid methane engine to measure the engine’s performance for future use with in-space vehicles.

Last month, eight altitude chamber tests were performed using an Aerojet workhorse engine to gather design data for future lander and in-space engines. Using the altitude chamber, which simulates the space-type vacuum environment, engineers were able to attach a larger nozzle and vary the propellant mixture ratios to test the engine's overall operating capability. This technology could be selected for future use with vehicles designed for transport, descent, or ascent to another planetary body or asteroid.”

Why do we test?  In the words of a good engineer, “it makes us look kind of professional.”

Link here.