Thanks for responding. Oh...god. i need to read THE list. I happily skipped the MGMAT's chapter on idioms, thinking its not needed.
Time to get back to idioms.
Yes, idioms are very much tested on the GMAT. It is the US centric idioms that are not being tested on the GMAT anymore.
For example, US-centric phrases that non-natives may not be conversant with such as ‘to do an end run’ or ‘to hold the line’ are not tested on the GMAT now(earlier also they were rarely tested but they have been eliminated altogether now). However, idioms as combination of words that must be used together to be correct such as regard as or prohibit from are still being tested on the GMAT.