A data processing device is configured so that, in a test mode of operation, the phase of an output signal of a second programmable delay module (PDM) is based on the phase of the input signal of the first PDM. To test the first and second PDMs, the output signal of the first PDM is set to each of a first set of phases and the corresponding phase of the output signal of the second PDM is compared to determine whether the performance of the first and second PDMs match a specification. Accordingly, the first and second PDMs are qualified based on their relative performance, reducing the need for test structures that consume an undesirably large amount of area.