Test Polarity: Detecting Positive and Negative Tests
André Hora · 2024
Positive tests (aka, happy path tests) cover the expected behavior of the program, while negative tests (aka, unhappy path tests) check the unexpected behavior. Ideally, test suites should have both positive and negative tests to better protect against regressions. In practice, unfortunately, we cannot easily identify whether a test is positive or negative. A better understanding of whether a test suite is more positive or negative is fundamental to assessing the overall test suite capability in testing expected and unexpected behaviors. In this paper, we propose test polarity, an automated approach to detect positive and negative tests. Our approach runs/monitors the test suite and collects runtime data about the application execution to classify the test methods as positive or negative. In a first evaluation, test polarity correctly classified 117 tests as as positive or negative. Finally, we provide a preliminary empirical study to analyze the test polarity of 2,054 test methods from 12 real-world test suites of the Python Standard Library. We find that most of the analyzed test methods are negative (88%) and a minority is positive (12%). However, there is a large variation per project: while some libraries have an equivalent number of positive and negative tests, others have mostly negative ones.