I know there is a glucose fasting test whereby your blood is tested and then you drink a glass of glucose water and test again. However I did not know there was a test for measuring the level of glucose tolerance. But I've never heard of a test for actually measuring insulin resistance.
There is a test (sorry forgotten its fullname) for measuring the amount of insulin produced.
Kraft used it for 30 years, and called it an Insulin Assay, I think. Not used in the UK to my knowledge.
The key thing would be how much insulin was needed to deal with the glucose in (for example) an oral glucose tolerance test.
If a 'normal' produces x amount, to keep blood glucose 'normal' during test.
and a 'insulin resistant person' used x + extra insulin to keep bg 'normal' then that person has a measurable amount of insulin resistance. The key thing is that their insulin resistance will not show up as glucose intolerance and raised bgs, because they are pumping out enough insulin to keep bg 'normal' with the knock on effect that it causes insulin resistance.
You may find this video interesting.