What we know about software testability: a survey.

Software testability is the degree to which a software system or a unit under test supports its own testing. To predict and improve software testability, a large number of techniques and metrics have been proposed by both practitioners and researchers in the last several decades. Reviewing and getting an overview of the entire state-of-the-art and -practice in this area is often challenging for a practitioner or a new researcher. Our objective is to summarize the state-of-the-art and -practice in this area and to benefit the readers (both practitioners and researchers) in preparing, measuring and improving software testability. To address the above need, we conducted a survey in the form of a systematic literature mapping (classification) in this area. After compiling an initial pool of 303 papers, a systematic voting was conducted among the authors, and our final pool included 208 papers. The area of software testability has been comprehensively studied by researchers and practitioners. Approaches for measurement of testability and improvement of testability are the most-frequently addressed in the papers. The two most often mentioned factors affecting testability are observability and controllability. Common ways to improve testability are testability transformation, improving observability, adding assertions, and improving controllability. The results could help practitioners measure and improve software testability in their projects. To assess potential benefits of this review paper, we shared its draft version with two of our industrial collaborators. They mentioned that they found the review useful and beneficial in their testing activities. Our results can also benefit researchers in observing the trends in this area and identify the topics which need further investigations.