  Advances in ubiquitous computing have enabled end-user authoring of
context-aware policies (CAPs) that control smart devices based on specific
contexts of the user and environment. However, authoring CAPs accurately and
avoiding run-time errors is challenging for end-users as it is difficult to
foresee CAP behaviors under complex real-world conditions. We propose
Fast-Forward Reality, an Extended Reality (XR) based authoring workflow that
enables end-users to iteratively author and refine CAPs by validating their
behaviors via simulated unit test cases. We develop a computational approach to
automatically generate test cases based on the authored CAP and the user's
context history. Our system delivers each test case with immersive
visualizations in XR, facilitating users to verify the CAP behavior and
identify necessary refinements. We evaluated Fast-Forward Reality in a user
study (N=12). Our authoring and validation process improved the accuracy of
CAPs and the users provided positive feedback on the system usability.
