India's enormous foreign exchange reserves faces its biggest test in the next 12 months as a record $256 billion of total overseas debt comes up for repayment amid a possible flight of capital due to monetary tightening by the Federal Reserve. External debt worth $256 billion matures over the next 12 months, according to the September data released by the finance ministry. This is about 43 per cent of the September external debt outstanding at $596 billion.