Quote: I took this test years ago and ended up (I think) as an ISTJ. Does anyone know if this test is proven to be stable over time, or is there some sort of expected variation?
I think the full test (2+ hours, administered by a psychologist) is pretty darn stable, although people do tend to moderate their personalities as they age.
The quickie online tests are a little less stable, since people do have a tendency to contrast themselves with who is around them. For instance, you might be moderately E, but if you're surrounded by a bunch of extreme E's, you might judge yourself as an I on a quick test.
It sounds like you're strongly TJ, but the I vs. E and S vs. N thing is a little more ambiguous. You might want to check out the profiles of all the types that might apply to you - sometimes one will jump out at you!