Generating external synchronizable test sequences that detect output-shifting faults

Synchronization problems arise when testing distributed systems. For some specifications, there is no synchronizable test sequence, and external synchronization operations between testers are unavoidable. Test sequences that involve external synchronization operations to solve synchronization problems are called external synchronizable test sequences. Another problem in distributed testing is that output-shifting faults are difficult to detect. Most external synchronizable test sequences generated by former methods cannot detect output-shifting faults. A synchronization transition digraph and a synchronization relation digraph are presented to describe the protocol specification under test and the communication channels between testers, respectively. A method of generating external synchronizable test sequences based on these two digraphs, which considers the costs of external synchronization operations, is also presented. It could generate test sequences that detect output-shifting faults. Furthermore, it does neither require the testers full-meshed, nor require the costs of communication channels between testers identical.