Interestingly, it is being said that at least one of India's nuclear tests back in 1998 actually failed and one of the scientists is therefore advocating that India not sign the Comprehensive Test Ban Treaty until it has established a 'credible nuclear deterrent'. A more detailed article is available here.
Quite frankly, I find that argument baloney. Pakistan, India's principle threat, knows that India has plenty of nuclear bombs that are sufficiently functional. A single failed test shouldn't delay India from signing onto the CTBT. Moreover, India needs to consider whether its continued defiance of the international nuclear community will cause its newly re-established suppliers to reconsider their decision to abandon the virtual trade embargo placed on India after their initial nuclear tests.
India, lacking any real indigenous sources of uranium, requires trade to be able to maintain their nuclear power plants. Increases in power demands and the construction of additional nuclear power plants will only serve to increase the demand for uranium and while thorium based cycles are showing progress they cannot serve to replace uranium altogether.
Further nuclear tests would only serve to undermine India's current status with the USA and with the international community and highlight India's dependence on foreign sources for its uranium. They would not, in my opinion, further any military or national defence goals.