[HADOOP-13716] Add LambdaTestUtils class for tests; fix eventual consistency problem in contract test setup

• Type: New Feature
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 2.8.0
• Fix Version/s: 2.8.0, 3.0.0-alpha2
• Component/s: test
• Target Version/s: 2.8.0, 3.0.0-alpha2
• Hadoop Flags: Reviewed
• Assignee: Steve Loughran
• Reporter: Steve Loughran
• Created: 12/Oct/16 19:48
• Updated: 24/Oct/16 17:18
• Resolved: 24/Oct/16 17:18

Description

To make our tests robust against timing problems and eventual consistent stores, we need to do more spin & wait for state.

We have some code in GenericTestUtils.waitFor to await a condition being met, but the predicate it calls doesn't throw exceptions, there's no way for a probe to throw an exception, and all you get is the eventual "timed out" message.

We can do better, and in closure-ready languages (scala & scalatest, groovy and some slider code) we've examples to follow. Some of that work has been reimplemented slightly in S3ATestUtils.eventually

I propose adding a class in the test tree, Eventually to be a successor/replacement for these.

1. has an eventually/waitfor operation taking a predicate that throws an exception
2. has an "evaluate" exception which tries to evaluate an answer until the operation stops raising an exception. (again, from scalatest)
3. plugin backoff strategies (from Scalatest; lets you do exponential as well as linear)
4. option of adding a special handler to generate the failure exception (e.g. run more detailed diagnostics for the exception text, etc).
5. be Java 8 lambda expression friendly
6. be testable and tested itself.

Issue Links

• is depended upon by: HADOOP-13713 ITestS3AContractRootDir.testRmEmptyRootDirNonRecursive failing intermittently