Github user twalthr commented on a diff in the pull request:
https://github.com/apache/flink/pull/4454#discussion_r131100075
--- Diff: docs/dev/testing.md ---
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+---
+title: "Testing"
+nav-parent_id: dev
+nav-pos: 110
+---
+<!--
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+
+This page briefly discusses how to test Flink application in the local
environment.
+
+* This will be replaced by the TOC
+{:toc}
+
+## Unit testing
+
+It is encouraged to test your classes with unit tests as much as possible.
For example if one implement following `ReduceFunction`:
+~~~java
--- End diff --
Usually, we implement code examples in both Scala and Java.
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