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When developers make changes to their code, they typically run regression tests to detect if their recent changes (re)introduce any bugs. However, many tests are flaky, and their outcomes can change non-deterministically, failing without apparent cause. Flaky tests are a significant nuisance in the development process, since they make it more difficult for developers to trust the outcome of their tests. The traditional approach to identify flaky tests is to rerun them multiple times: if a test is observed both passing and failing on the same code, it is definitely flaky. We conducted a very large empirical study looking for flaky tests by rerunning the test suites of 24 projects 10,000 times each, and found that even with this many reruns, some flaky tests were still not detected. We propose FlakeFlagger, a novel approach that collects a set of features describing the behavior of each test, and then predicts tests that are likely to be flaky based on similar behavioral features. We found that FlakeFlagger correctly labeled at least as many tests as flaky as a state-of-the-art flaky test classifier, but that FlakeFlagger reported far fewer false positives (an increase in precision from just 11% to 60%). This lower false positive rate translates directly to saved time for researchers and developers who use the classification result to guide more expensive flaky test detection processes. By investigating the information gain of each feature, we conclude that test execution time, overall test coverage, coverage of recently changed lines and usage of third party libraries are effective predictors of test flakiness. We did not find any keywords or tokens in the source code of tests that were effective in predicting test flakiness, and did not find the presence of test smells to be effective in predicting test flakiness. This archive contains the dataset that we collected of flaky tests, along with the features that we collected from each test. Contents: Project_Info.csv: List of projects and their revisions studied build-logs-<project-slug>.tgz: An archive of all of the maven build logs from each of the 10,000 runs of that project's test suite. failing-test-reports-<project-slug>.tgz An archive of all of the surefire XML reports for each failing test of each build of each project. test_results.csv: Summary of the number of passing and failing runs for each test in each project. "Run ID" is a key into the <project-slug>.tgz archive also in this artifact, which refers to the run that we observed the test fail on. test_features.csv: Summary of the features that each test had, as per our feature detectors described in the paper flakeflagger-code.zip: All scripts used to generate and process these results. These scripts are also located at https://github.com/AlshammariA/FlakeFlagger
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A large-scale longitudinal study of flaky tests
Flaky tests are tests that can non-deterministically pass or fail for the same code version. These tests undermine regression testing efficiency, because developers cannot easily identify whether a test fails due to their recent changes or due to flakiness. Ideally, one would detect flaky tests right when flakiness is introduced, so that developers can then immediately remove the flakiness. Some software organizations, e.g., Mozilla and Netflix, run some tools—detectors—to detect flaky tests as soon as possible. However, detecting flaky tests is costly due to their inherent non-determinism, so even state-of-the-art detectors are often impractical to be used on all tests for each project change. To combat the high cost of applying detectors, these organizations typically run a detector solely on newly added or directly modified tests, i.e., not on unmodified tests or when other changes occur (including changes to the test suite, the code under test, and library dependencies). However, it is unclear how many flaky tests can be detected or missed by applying detectors in only these limited circumstances. To better understand this problem, we conduct a large-scale longitudinal study of flaky tests to determine when flaky tests become flaky and what changes cause them to become flaky. We apply two state-of-theart detectors to 55 Java projects, identifying a total of 245 flaky tests that can be compiled and run in the code version where each test was added. We find that 75% of flaky tests (184 out of 245) are flaky when added, indicating substantial potential value for developers to run detectors specifically on newly added tests. However, running detectors solely on newly added tests would still miss detecting 25% of flaky tests. The percentage of flaky tests that can be detected does increase to 85% when detectors are run on newly added or directly modified tests. The remaining 15% of flaky tests become flaky due to other changes and can be detected only when detectors are always applied to all tests. Our study is the first to empirically evaluate when tests become flaky and to recommend guidelines for applying detectors in the future.
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- PAR ID:
- 10601348
- Publisher / Repository:
- Association for Computing Machinery (ACM)
- Date Published:
- Journal Name:
- Proceedings of the ACM on Programming Languages
- Volume:
- 4
- Issue:
- OOPSLA
- ISSN:
- 2475-1421
- Format(s):
- Medium: X Size: p. 1-29
- Size(s):
- p. 1-29
- Sponsoring Org:
- National Science Foundation
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