Software Architect's Handbook

Isolability

Isolability is the degree to which a component can be isolated. The goal is to have tests that can focus on specific pieces of functionality (for example, unit tests) that do not have dependencies on other components. This allows us to create and execute tests on a completed component, even if other components are not complete.

We want to avoid a situation where we have to write a great deal of code before any of it can be tested since it is desirable to get feedback as quickly as possible. If a problem is found, it will be easier to determine its source and cause if components exhibit isolability.

An increase in isolability increases the testability of a component.