Well, I was thinking of shooting a flare test outdoors today but it's raining and I don't want to get the step tablets wet...

I was looking forward to discussing subtle differences that different tests might reveal, for example...

LP Clerc describes the difference of flare indoors versus outdoors. Indoors your subject lighted by photofloods is well lit but the surroundings are dark = less flare. Outdoors your subject is lit by sun, cloud or open sky... but the background may be bright open sky = more flare.

With a lens shade and controlled lighting indoors, the flare would be "different" than it would be without a lens shade. Outdoors open sky will send many rays into the lens which aren't aimed directly at the film plane. Some of these rays will be scattered by the optics and camera internal reflections. Flare would illuminate the entire camera chamber.

It wouldn't invalidate the test done indoors. Just that different scenarios would give different results, which is exactly the problem Flare poses.