What would cause outlets and switches to have a static shock when tested or flipped, occurs on second floor only. All switches and outlets work and test out. It’s not a strong shock, just like static.
Dry air, low humidity.
I would add carpet. 
I will tell you what, the new supermarket (publix) they just built had a TERRIBLE problem with that, I could not go in without getting shocked every time I touched a metal cabinet. I could also shock everyone I touched. Pretty annoying.
I never found it in a residential home thought ( to any great extent)
I know that these are some of the causes, is there any time when it could be caused by stray electrical current? Or would a bigger jolt be felt?
I know exactly what you mean, the local COSTCO (which I love), gives me quite a shock every time I open the cold section doors. Sometimes it’s a good jolt!
I agree with Linus. The cold air can’t hold moisture and thus gets “dry”. It happens here this time of year since the temp drops. We get lots of static so I run a humidifier and it reduces the static. The shock comes from the electricity from your body jumping to the screw that holds the faceplate on. At one time I was nylon screws sold to prevent that from happening.
Type of foot wear, type of carpet, Low humidity are all causes . there is a antic static spray you can help reduce it. grounding yourself before entering the area can reduce it.
(Can not wait for responses for this post .)
You can actually buy shoe covers with a conductive strip on the bottom.
They are used in surgical suites with conductive floors where flammable anesthetics are used.
Not as common as they used to be.
I used to have to test this type of floor monthly.