Understanding Test Convention Consistency as a Dimension of Test Quality

Unit tests must be readable to help developers understand and evolve production code. Most existing test quality metrics assess test code's ability to detect bugs. Few metrics focus on test code's readability. One standard approach to improve readability is the consistent application of conventions. We investigated test convention consistency as a dimension of test quality. We formalized test suite consistency as the extent to which alternatives are used within a code base and introduce two complementary metrics to capture this extent. We elaborated a catalog of over 30 test conventions for the Java language organized in 10 convention classes that group mutual alternatives. We developed tool support to detect occurrences of conventions, compute consistency metrics over a test suite, and view occurrences of conventions in the corresponding code. We applied our tools to study the consistency of the test suites of 20 large open source Java projects. The study validates the design of the test convention classes, provides descriptive statistics on the range of consistency values for 10 different convention classes, and enables us to link observed changes in consistency values to specific events in the change history of our target systems, thus providing evidence of the construct validity of the metrics. We conclude that analyzing test suite consistency via static analysis shows promise as a practical approach to help improve test suite quality.