  Manual testing, as a complement to automated GUI testing, is the last line of
defense for app quality especially in spotting usability and accessibility
issues. However, the repeated actions and easy missing of some functionalities
make manual testing time-consuming, labor-extensive and inefficient. Inspired
by the game candy crush with flashy candies as hint moves for players, we
develop a tool named NaviDroid for navigating human testers via highlighted
next operations for more effective and efficient testing. Within NaviDroid, it
constructs an enriched state transition graph (STG) with the trigger actions as
the edges for two involved states. Based on the STG, NaviDroid utilizes the
dynamic programming algorithm to plan the exploration path, and augment the
run-time GUI with visualized hint moves for testers to quickly explore untested
states and avoid duplication. The automated experiments demonstrate the high
coverage and efficient path planning of NaviDroid. A user study further
confirms its usefulness in the participants covering more states and
activities, detecting more bugs within less time compared with the control
group. NaviDroid demo video: https://youtu.be/lShFyg_nTA0.
