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add expectations for flaky test issues

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Daniel Smith 2016-01-22 16:10:13 -08:00
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@ -32,7 +32,93 @@ Documentation for other releases can be found at
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# Hunting flaky tests in Kubernetes
# Flaky tests
Any test that fails occasionally is "flaky". Since our merges only proceed when
all tests are green, and we have a number of different CI systems running the
tests in various combinations, even a small percentage of flakes results in a
lot of pain for people waiting for their PRs to merge.
Therefore, it's very important that we write tests defensively. Situations that
"almost never happen" happen with some regularity when run thousands of times in
resource-constrained environments. Since flakes can often be quite hard to
reproduce while still being common enough to block merges occasionally, it's
additionally important that the test logs be useful for narrowing down exactly
what caused the failure.
Note that flakes can occur in unit tests, integration tests, or end-to-end
tests, but probably occur most commonly in end-to-end tests.
## Filing issues for flaky tests
Because flakes may be rare, it's very important that all relevant logs be
discoverable from the issue.
1. Search for the test name. If you find an open issue and you're 90% sure the
flake is exactly the same, add a comment instead of making a new issue.
2. If you make a new issue, you should title it with the test name, prefixed by
"e2e/unit/integration flake:" (whichever is appropriate)
3. Reference any old issues you found in step one.
4. Paste, in block quotes, the entire log of the individual failing test, not
just the failure line.
5. Link to durable storage with the rest of the logs. This means (for all the
tests that Google runs) the GCS link is mandatory! The Jenkins test result
link is nice but strictly optional: not only does it expire more quickly,
it's not accesible to non-Googlers.
## Expectations when a flaky test is assigned to you
Note that we won't randomly assign these issues to you unless you've opted in or
you're part of a group that has opted in. We are more than happy to accept help
from anyone in fixing these, but due to the severity of the problem when merges
are blocked, we need reasonably quick turn-around time on test flakes. Therefore
we have the following guidelines:
1. If a flaky test is assigned to you, it's more important than anything else
you're doing unless you can get a special dispensation (in which case it will
be reassigned). If you have too many flaky tests assigned to you, or you
have such a dispensation, then it's *still* your responsibility to find new
owners (this may just mean giving stuff back to the relevant Team or SIG Lead).
2. You should make a reasonable effort to reproduce it. Somewhere between an
hour and half a day of concentrated effort is "reasonable". It is perfectly
reasonable to ask for help!
3. If you can reproduce it (or it's obvious from the logs what happened), you
should then be able to fix it, or in the case where someone is clearly more
qualified to fix it, reassign it with very clear instructions.
4. If you can't reproduce it: __don't just close it!__ Every time a flake comes
back, at least 2 hours of merge time is wasted. So we need to make monotonic
progress towards narrowing it down every time a flake occurs. If you can't
figure it out from the logs, add log messages that would have help you figure
it out.
# Reproducing unit test flakes
Try the [stress command](https://godoc.org/golang.org/x/tools/cmd/stress).
Just
```
$ go install golang.org/x/tools/cmd/stress
```
Then build your test binary
```
$ godep go test -c -race
```
Then run it under stress
```
$ stress ./package.test -test.run=FlakyTest
```
It runs the command and writes output to `/tmp/gostress-*` files when it fails.
It periodically reports with run counts. Be careful with tests that use the
`net/http/httptest` package; they could exhaust the available ports on your
system!
# Hunting flaky unit tests in Kubernetes
Sometimes unit tests are flaky. This means that due to (usually) race conditions, they will occasionally fail, even though most of the time they pass.