Testing is the most commonly used approach to the assurance of software quality and reliability. The testing of object-oriented software is much more complex than that of conventional programs. Although we proposed previously a method called TACCLE for testing object-oriented software at the class and cluster levels, it did not cover concurrent or non-deterministic situations. This paper puts forward a strategy for selecting synchronization sequences to test concurrent object-oriented software, including non-deterministic cases. It is based on OBJSA net/CLOWN specifications. Experiments have been carried out in a case study to verify the efficacy of the strategy.