Dependability is an important attribute for microfluidic biochips that are used for safety-critical applications, such as point-of-care health assessment, air-quality monitoring, and food-safety testing. Therefore, these devices must be adequately tested after manufacture and during bioassay operations. Known techniques for biochip testing are all function oblivious (i.e., while they can detect and locate defect sites on a microfluidic array, they cannot be used to ensure correct operation of functional units). In this paper, we introduce the concept of functional testing of microfluidic biochips. We address fundamental biochip operations, such as droplet dispensing, droplet transportation, mixing, splitting, and capacitive sensing. Long electrode actuation times are avoided to ensure that there is no electrode degradation during testing. The functional testing of pin-constrained biochips is also studied. We evaluate the proposed test methods using simulations as well as experiments for a fabricated biochip.