Like the report said, they were carful to stay in international waters and then went to Sri Lanka. Besides the fact that they focused on the missile test, IN should be worried about this the most. Once because they could operate that close for so many days undetected, secondly that they were maping the sea area, which clearly hints on gathering data for sub operations.
Imo IN is focusing too much on big carriers, nuclear subs and strangely on landing operations, while the maritime surveillance and anti sub warfare is struggeling.
The 12 x P8Is are not enough for a force that has to cover such a large area, one reason why the delays of the medium range MPA procurment is not understandable and the same goes for shore based AWACS, UAVs, or the 2nd conventional sub order. With more MPAs and AWACS these ships can be detected and monitored way earlier and faster, than with naval vessels on IN, or ICG.
I do agree that we need nuclear subs and bigger carriers for a credible deterrance against china (although I don't think we need landing capabilities in this regard), but the first step should be to secure our coast lines and area of interest, before we deploy forces anywhere closer to the Chinese mainland. Especially more cost-effective MPAs, long endurance UAVs and way more conventional subs are need, if we want to counter the thread, but as usual everything is running very slow.