Show tracing output only for failed tests #959
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Lorak-mmk
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Before, tracing crate's prints weren't captured during tests. Those with error level used to bloat tests' output, which was especially painful in CI. OTOH, we wanted to have traces visible in failed tests in order to easier spot the cause of a failure. By using tracing_subscriber's TestWriter, tracing's prints are now captured and only shown if a test fails. This enables efficient troubleshooting especially in case of flaky tests, as those are common in CI only and hard to be reproduced locally. For all tests to easily use the captured tracing, a function setup_tracing() is introduced. This commit adds it to scylla crate unit tests. Integration tests and proxy tests are covered in next commits.
As described in the previous commit, setup_tracing() enables captured trace output for tests. Not to make scylla crate depend on tracing_subscriber (now it's only a dev-dependency), the function is simply copied to integration/utils.rs. Integration tests are made call that function at the beginning.
As explained in previous commits, setup_tracing() enables captured tracing outputs in tests.
...so that new tests have setup_tracing() added. Co-authored-by: Karol Baryła <[email protected]>
Now, iff a test fails in the CI, all its logs are preserved and available for further investigation.
It sometimes happens that a test with a random seed fails (especially in the CI). With this debug print and previous commits enabling tracing capturing, debugging such a case should be easier now.
The test was originally created for round-robin default load balancing policy. As the current default policy randomly picks a replica instead, the test became flaky. To mitigate this and still check that various replicas are queried in the non-LWT case: - number of iterations is increased from 15 to 30; - asserted condition is weakened: so far we asserted that all replicas were queried; now more-than-one replica suffice.
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Lorak-mmk
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Motivation
Flaky tests keep disrupting our CI. Those test failures are often difficult to reproduce locally. A way is needed to debug tests that failed in CI.
On the other hand, error traces bloat outputs.
What's done
tracing_subscriber'sTestWriter,tracing's prints are now captured and only shown if a test fails;setup_tracing()is introduced and added to most tests inscyllaandscylla-proxycrates.CONTIBUTING.mdis updated to mentionsetup_tracing()'s intended usage.Pre-review checklist
[ ] I added relevant tests for new features and bug fixes.[ ] I have provided docstrings for the public items that I want to introduce.[ ] I have adjusted the documentation in./docs/source/.[ ] I added appropriateFixes:annotations to PR description.