Skip to content
Software Architecture Guide

Testability

Explanation

Section titled “Explanation”

Testability is the degree to which a system, or a part of it under test, supports its own testing. In other words, the system helps you test it.

When testability is high, finding faults by testing is easier. A fault is a defect in the software (see Fault). When testability is low, the team needs more test effort.

Observability. Observability is a core part of testability. It means you can see test results, both intermediate and final. If a tester cannot see what the system did, they cannot judge whether it worked.

Standard definition. The ISO/IEC 25010 quality model (see ISO/IEC 25010 Product Quality Model) describes testability as how effectively and efficiently you can establish test criteria for a system, product or component.

Where it sits. ISO 25010 places testability under maintainability. Maintainability is about how effectively and efficiently you can modify a product. The arc42 quality model notes this placement. It argues that testability also belongs under reliability, so it should appear in both places.

Why it matters. When you maintain or change a system, testability reduces risk.

Example

Section titled “Example”

A team builds an order system. Testers can see the intermediate results of a price calculation, not only the final total. When a total is wrong, they see which step failed. In a system that shows only the final total, the same fault takes longer to find. That system has lower testability and needs more test effort.

Checks

Section titled “Checks”
  • The document states how testers can observe intermediate and final results of the system.
  • Testability is listed as a quality goal where changes to the system are expected, with its link to risk reduction.
  • Testability is treated under maintainability and also considered under reliability.
Section titled “Related”

Sources

Section titled “Sources”