Recently paper-based microfluidic chips have been proposed to achieve microfluidic analysis for many applications. Such chips achieve "lab-on-paper" instead of traditional "lab-on-chips". The paper substrate is attractive because it is cost-effective, easy to use and disposable, fully compatible with most medical/biochemical applications, and offering liquid flow by capillary without being relied on external forces and equipment. Test methods for digital microfluidic (DMF) biochips have been studied for years; however, they are developed for traditional DMF chips and thus are not directly applicable to paper-based DMF (PB-DMF) chips. In PB-DMF chips, electrodes are control wires are printed on the same paper surface, while electrodes can be placed with custom structure. In this paper, we present test and diagnosis methods for faults in PB-DMF. A design-for-diagnosability scheme is proposed, and it is shown that single faults can be located and tolerated by providing alternative paths in PB-DMF chips. The feasibility of the proposed method is validated through experiments.