The Effect of Test-Driven Development on Program Code

Usage of test-driven development (TDD) is said to lead to better testable programs. However, no study answers either the question how this better testability can be measured nor whether the feature of better testability exists. To answer both questions we present the concept of the controllability of assignments. We studied this metric on various TDD and conventional projects. Assignment controllability seems to support the rules of thumb for testable code, e.g. small classes with low coupling are better testable than large classes with high coupling. And as opposed to the Chidamber and Kemerer metric suite for objectoriented design, controllability of assignments seems to be an indicator whether a project was developed with TDD or not.