Paradise, I personally think nobody in this world has to courage to do one more nuclear test other than some rogue countries such as Iran, Isreal, N.Korea. Not even US I guess. However the best option would be as you said supercomputer simulation of nuclear tests. I guess only US and Russia has the simulation capability till date.
Regarding the investment of billions of dollars, why US is hell bent on nuclear deal than India? Apart from ensuring India's backdoor entry on NPT and CTBT it is Business. Business should be Win-Win situation. India should be clever enough to achieve that. If you pull, you also loose.
