Mechanical architecture decisions are usually driven by familiar priorities: performance, packaging, cost, manufacturability, assembly, reliability, and interfaces. Verification comes later, once the design is mature enough for teams to define detailed protocols and build representative hardware.
But the ability to test a product is often determined much earlier.
As discussed in our article The Most Expensive Decision Before Prototype 1, early architectural choices can establish constraints that become increasingly expensive to change as development progresses. Testability is one of those considerations.
Architecture dictates what engineers can access, instrument, isolate, load, measure, and replace. By the time a team discovers that a critical performance characteristic is difficult to verify or diagnose, changing those architectural decisions may be expensive.
Testability therefore deserves a place in architecture development itself.
Architecture Determines What You Can Learn
Testability means more than having a way to put the finished product on a test stand.
Consider what happens when a system fails. Engineers need to isolate the subsystem responsible, measure loads at critical interfaces, and reproduce representative boundary conditions. Substituting known-good components may help narrow the investigation, while independent testing can distinguish a component failure from an interaction between several components. The ease of performing these activities depends heavily on the mechanical architecture.
A highly integrated assembly might provide excellent packaging and structural performance while leaving critical interfaces inaccessible. A load path might work perfectly in the finished system but be difficult to reproduce at the component level. Multiple functions might be combined into one component, making it difficult to determine which function caused a system-level failure.
None of these choices necessarily represents poor design. They do, however, affect how easily the team can learn from the hardware.
Poor Testability Turns Failures Into System-Level Mysteries
A verification failure should generate useful information. Sometimes it generates little more than confirmation that the product failed.
When architecture prevents engineers from isolating variables, the investigation expands. Teams add instrumentation, develop new fixtures, perform destructive teardown, modify prototypes, or build additional hardware specifically to separate competing hypotheses.
Then the test must often be repeated.
The resulting cost extends well beyond the additional testing. The development team loses time while trying to determine what the original test actually revealed.
This is particularly consequential when prototype quantities are limited or system-level hardware is expensive. Every test article becomes a scarce source of information. An architecture that makes failures difficult to diagnose reduces how much the team can learn from each one.
Integration Creates a Testability Tradeoff
Maximum modularity carries its own tradeoffs. Integrated mechanical architectures can provide substantial benefits in mass, stiffness, packaging, reliability, part count, and cost. Separating every function simply to make testing easier could compromise the product the team is trying to develop.
The more useful question is what diagnostic capability the team gives up when functions become tightly integrated.
That tradeoff deserves consideration alongside the other architectural decisions being made. For high-risk functions in particular, teams should be able to answer a simple question:
If this feature fails verification, how will we determine what caused it?
If the answer requires a completed system, extensive teardown, or a new generation of specialized test hardware, the architecture may be creating development risk that is not yet visible.
Bring Verification Thinking Into Architecture Decisions
Teams do not need finished verification protocols during architecture development. They do need to understand how the most important and highest-risk performance claims will eventually be demonstrated and diagnosed.
As discussed in Verification Is a System, Not a Phase, effective verification depends on decisions made throughout development, including requirements, risk analysis, and engineering design.
Architecture reviews can consider whether critical interfaces are accessible for instrumentation, whether important functions can be isolated, how representative loads and boundary conditions will be created, and what diagnostic paths will remain available after a failure.
They can also ask whether meaningful testing can begin before the entire system exists. Component- and subsystem-level learning can be particularly valuable when it allows teams to challenge assumptions before expensive integrated prototypes are built.
The objective is to give testability appropriate weight among the other architectural inputs. Manufacturability, assembly, serviceability, cost, and performance still matter, but the team should understand how its architectural choices will affect its ability to test and diagnose the product.
Architecture Should Support Learning
Mechanical architecture shapes more than the finished product. It also shapes the development team’s ability to understand that product.
A program needs an architecture capable of meeting its requirements. It also needs enough access, isolation, and diagnostic capability to determine whether those requirements are being met, understand why they are not, and identify what needs to change.
The architecture defines the product, but it also determines how effectively the team can learn from it.
Is Your Architecture Designed to Learn?
A65 Consulting offers a free testability analysis for medical device development teams. We evaluate mechanical architecture, critical interfaces, instrumentation access, functional isolation, and diagnostic pathways to identify where design decisions may make verification more difficult, expensive, or time-consuming.
If your team is developing its mechanical architecture, preparing for prototypes, or planning verification, contact A65 Consulting to schedule a complimentary testability analysis. We also offer fractional engineering leadership for organizations seeking experienced technical direction, strategic guidance, and hands-on leadership without the commitment of a full-time executive.
Email: sdonnigan@a65consulting.com
Or schedule your review online
References
- NASA. Inattention to Testability Can Complicate Verification Efforts. NASA Lessons Learned Information System, Lesson 2050.
- International Council on Systems Engineering (INCOSE). Systems Engineering Handbook: A Guide for System Life Cycle Processes and Activities. 5th ed., Wiley, 2023.
- Engel, Avner. Verification, Validation, and Testing of Engineered Systems. Wiley, 2010.
- Ulrich, Karl T., Steven D. Eppinger, and Maria C. Yang. Product Design and Development. 7th ed., McGraw Hill, 2020.
- Pahl, Gerhard, et al. Engineering Design: A Systematic Approach. 3rd ed., Springer, 2007.