Structural testing of digital microfluidic biochips targets the detection of physical defects, but it does not guarantee robust execution of target bioassays or the integrity of assay outcomes. Functional testing is needed to detect fluidic malfunctions. Such tests ensure whether or not, the elementary fluidic operations, such as droplet transportation, mixing, incubation, and splitting are reliably executed on the microfluidic array. Routing test and mixing/splitting test are two important steps in functional testing. We present two procedures for optimal bidirectional routing test and accelerated mixing/splitting test. Compared to previous methods, these procedures need significantly fewer droplet manipulation steps and reduced execution time. The proposed method of functional testing in an N x N microfluidic array requires only a constant number of mixing/splitting steps. Further, the test outcome is free from boundary errors related to droplet size that may arise during mixing/splitting test.