Valuable Unit Tests in a Software Medical Device, Part 8

The Traceability Matrix

A critical factor in making unit tests usable in an auditable manner is incorporating them into the traceability matrix. As with any test, requirements, design elements and hazards must be traced to one another through use of the traceability matrix.

The project team must document traceability of requirements through specification and testing to ensure that all requirements have been tested and correctly implemented (product requirements traceability matrix).

Thomas H. Farris, Safe and Sound Software

Our SOPs and work instructions will require that we prove traceability of our tests and test results, whether manual or automated unit tests. Just as has always been done with the manual tests that we are familiar with, tests must be traced to software requirements, design specifications, hazards and risks. The goal is simply to prove that we have tested that which we have designed and implemented, and in the case of automated tests this is all very easy to achieve!

Do We Still Need Manual Tests?

Yes! Absolutely! There are a number of reasons why manual tests are still, and always will be, required: Installation Qualification and environmental tests. Both manual and automated tests are valid and valuable, and neither should be considered a replacement for the other.

Manual tests allow for a certain amount of “creative” testing that may not be considered during unit test development. Manual tests also lead to greater insight related to usability and user interaction issues.

To this end, defect that is discovered during manual testing should result in an automated test.


  • Device Advice: Regulation and Guidance, Software Validation Guidelines,
  • Safe and Sound Software – Creating an Efficient and Effective Quality System for Software Medical Device Organizations, Thomas H. Farris. ASQ Quality Press, Milwaukee, Wisconsin, 2006
  • CFR – Code of Federal Regulations Title 21. Subpart C – Design Controls, Section 820.30 Design Controls
  • Agile Software Requirements, Dean Leffingwell. Addison-Wesley. Copyright © 2011, Pearson Education, Inc. Boston, MA
  • Continuous Delivery, Jez Humble, David Farley. Addison-Wesley, Copyright © 2011, Pearson Education, Inc. Boston, MA