I think your instinct is right: the dark glass is going to negate any test.
I always assumed that products like olive oil sold in thick green bottles were sensitive to degradation by (UV, sun)light, so if that is true then by definition a casual in store test is not going to work. But perhaps green bottles mean nothing vis a vis light.
I do recall that brown bottles were a thing in brewing to prevent beer from becoming funky by the action of light, but perhaps oils aren't susceptible to that.
I always assumed that products like olive oil sold in thick green bottles were sensitive to degradation by (UV, sun)light, so if that is true then by definition a casual in store test is not going to work. But perhaps green bottles mean nothing vis a vis light.
I do recall that brown bottles were a thing in brewing to prevent beer from becoming funky by the action of light, but perhaps oils aren't susceptible to that.