Github user pnowojski commented on a diff in the pull request:
https://github.com/apache/flink/pull/4454#discussion_r131900306
--- Diff: docs/dev/testing.md ---
@@ -0,0 +1,189 @@
+---
+title: "Testing"
+nav-parent_id: dev
+nav-id: testing
+nav-pos: 99
+---
+<!--
+Licensed to the Apache Software Foundation (ASF) under one
+or more contributor license agreements. See the NOTICE file
+distributed with this work for additional information
+regarding copyright ownership. The ASF licenses this file
+to you under the Apache License, Version 2.0 (the
+"License"); you may not use this file except in compliance
+with the License. You may obtain a copy of the License at
+
+ http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing,
+software distributed under the License is distributed on an
+"AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+KIND, either express or implied. See the License for the
+specific language governing permissions and limitations
+under the License.
+-->
+
+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
+public class SumReduce implements ReduceFunction<Long> {
+ @Override
+ public Long reduce(Long value1, Long value2) throws Exception {
+ return value1 + value2;
+ }
+}
+~~~
+
+it is very easy to unit test it with your favorite framework:
+
+~~~java
+public class SumReduceTest {
+ @Test
+ public void testSum() throws Exception {
+ SumReduce sumReduce = new SumReduce();
+
+ assertEquals(42L, sumReduce.reduce(40L, 2L));
+ }
+}
+~~~
+
+Or in scala:
+
+~~~scala
+class SumReduce extends ReduceFunction[Long] {
+ override def reduce(value1: java.lang.Long,
+ value2: java.lang.Long): java.lang.Long = value1 +
value2
+}
+~~~
+
+~~~scala
+class SumReduceTest extends FlatSpec with Matchers {
+ "SumReduce" should "add values" in {
+ val sumReduce: SumReduce = new SumReduce()
+ sumReduce.reduce(40L, 2L) should be (42L)
+ }
+}
+~~~
+
+## Integration testing
+
+You also can write integration tests that are executed against local Flink
mini cluster.
+In order to do so add a test dependency `flink-test-utils`.
+
+~~~ xml
+<dependency>
+ <groupId>org.apache.flink</groupId>
+ <artifactId>flink-test-utils{{site.scala_version_suffix}}</artifactId>
+ <version>{{site.version}}</version>
+</dependency>
+~~~
--- End diff --
Updated but it properties names depends on the user's `pom.xml` file.
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