1. In a data processing system, a method comprising: providing a plurality of test points located at predetermined circuit nodes; executing test code which includes a set of software-controllable interrupts; during execution of the test code, using a multiple input shift register (MISR) to accumulate data values from the plurality of test points to generate a MISR signature; determining one or more selected software-controllable interrupt types; and during execution of the test code, using the MISR to also accumulate data values from the plurality of test points during exception processing of one or more software-controllable interrupts within the set of software-controllable interrupts which are of the one or more selected software-controllable interrupt types to generate the MISR signature.