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

["Steve Loughran (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/HADOOP-13716?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Steve Loughran resolved HADOOP-13716.
-------------------------------------
    Resolution: Fixed

> Add LambdaTestUtils class for tests; fix eventual consistency problem in contract test setup
> --------------------------------------------------------------------------------------------
>
>                 Key: HADOOP-13716
>                 URL: https://issues.apache.org/jira/browse/HADOOP-13716
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: test
>    Affects Versions: 2.8.0
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>             Fix For: 2.8.0, 3.0.0-alpha2
>
>         Attachments: HADOOP-13716-001.patch, HADOOP-13716-002.patch, HADOOP-13716-003.patch, HADOOP-13716-005.patch, HADOOP-13716-006.patch, HADOOP-13716-branch-2-004.patch
>
>
> 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.
> # has an eventually/waitfor operation taking a predicate that throws an exception
> # has an "evaluate" exception which tries to evaluate an answer until the operation stops raising an exception. (again, from scalatest)
> # plugin backoff strategies (from Scalatest; lets you do exponential as well as linear)
> # option of adding a special handler to generate the failure exception (e.g. run more detailed diagnostics for the exception text, etc).
> # be Java 8 lambda expression friendly
> # be testable and tested itself.



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