Is Exceptional Behavior Testing an Exception?

Abstract

Software testing is a crucial activity to check the internal quality of a software. During testing, developers often create tests for the normal behavior of a particular functionality (e.g., was this file properly uploaded to the cloud?). However, little is known whether developers also create tests for the exceptional behavior (e.g., what happens if the network fails during the file upload?). To minimize this knowledge gap, in this paper we design and perform a mixed-method study to understand how 417 open source Java projects are testing the exceptional behavior using the JUnit and TestNG frameworks, and the AssertJ library. We found that 254 (60.91%) projects have at least one test method dedicated to test the exceptional behavior. We also found that the number of test methods for exceptional behavior with respect to the total number of test methods lies between 0% and 10% in 317 (76.02%) projects. Also, 239 (57.31%) projects test only up to 10% of the used exceptions in the System Under Test (SUT). When it comes to mobile apps, we found that, in general, developers pay less attention to exceptional behavior tests when compared to desktop/server and multi-platform developers. In general, we found more test methods covering custom exceptions (the ones created in the own project) when compared to standard exceptions available in the Java Development Kit (JDK) or in third-party libraries. To triangulate the results, we conduct a survey with 66 developers from the projects we study. In general, the survey results confirm our findings. In particular, the majority of the respondents agrees that developers often neglect exceptional behavior tests. As implications, our numbers might be important to alert developers that more effort should be placed on creating tests for the exceptional behavior.