This paper describes a versatile test facility developed by AECL for validation and reliability (V&R) testing of safety-critical software used in the process trip computers for CANDU reactors. It describes the hardware and software aspects of the test facility. The test hardware consists of a test rig with a test computer used for executing the test software and a process trip computer emulator. The test software is comprised of an operating system, a test interpreter, a test oracle, and a man-machine interface. This paper also discusses the application of the test facility in V&R testing of the process trip computer, how test scripts are prepared and automatically run on the test computer, and how test results are automatically generated by the test computer, thus eliminating potential human errors. The test scripts, which contain specific instructions for testing, are text files written in a special AECL test language. An AECL Test Language Interpreter (ATLIN) program interprets the test scripts and translates structured English statements in the test scripts into test actions. The intuitive nature of the special AECL test language, the version controlled test scripts in text format and automatic test logging feature facilitate the preparation of test cases, which are easy to repeat, review and readily modifiable, and production of consistent results. This paper presents the concept of adding a process trip computer emulator for use in preparation of V&R testing. The process trip computer emulator is designed independently from the actual process trip computer but based on the same functional specification as for the process trip computer. The use of the process trip computer emulator allows the test scripts to be exercised before the actual process trip computers are available for V&R testing, thereby, resulting in a significant improvement to the project schedule. The test facility, with the built-in process trip computer emulator, is also a valuable training tool for the V&R staff and plant personnel.