  We report our experience of using failure symptoms, such as error messages or
stack traces, to identify flaky test failures in a Continuous Integration (CI)
pipeline for a large industrial software system, SAP HANA. Although failure
symptoms are commonly used to identify similar failures, they have not
previously been employed to detect flaky test failures. Our hypothesis is that
flaky failures will exhibit symptoms distinct from those of non-flaky failures.
Consequently, we can identify recurring flaky failures, without rerunning the
tests, by matching the failure symptoms to those of historical flaky runs. This
can significantly reduce the need for test reruns, ultimately resulting in
faster delivery of test results to developers. To facilitate the process of
matching flaky failures across different execution instances, we abstract newer
test failure symptoms before matching them to the known patterns of flaky
failures, inspired by previous research in the fields of failure deduplication
and log analysis. We evaluate our symptom-based flakiness detection method
using actual failure symptoms gathered from CI data of SAP HANA during a
six-month period. Our method shows the potential of using failure symptoms to
identify recurring flaky failures, achieving a precision of at least 96%, while
saving approximately 58% of the machine time compared to the traditional rerun
strategy. Analysis of the false positives and the feedback from developers
underscore the importance of having descriptive and informative failure
symptoms for both the effective deployment of this symptom-based approach and
the debugging of flaky tests.
