doc: Add page for testing of EventSourcedBehavior, #27899 (#27902)

akka-docs/src/main/paradox/typed/persistence-testing.md

@@ -0,0 +1,65 @@
+# Testing
+
+## Dependency
+
+To use Akka Persistence and Actor TestKit, add the module to your project:
+
+@@dependency[sbt,Maven,Gradle] {
+  group1=com.typesafe.akka
+  artifact1=akka-persistence-typed_$scala.binary_version$
+  version1=$akka.version$
+  group2=com.typesafe.akka
+  artifact2=akka-actor-testkit-typed_$scala.binary_version$
+  version2=$akka.version$
+  scope2=test
+}
+
+## Unit testing
+
+Unit testing of `EventSourcedBehavior` can be done with the @ref:[ActorTestKit](testing-async.md)
+in the same way as other behaviors.
+
+@ref:[Synchronous behavior testing](testing-sync.md) for `EventSourcedBehavior` is not supported yet, but
+tracked in @github[issue #26338](#23712).
+
+You need to configure a journal, and the in-memory journal is sufficient for unit testing. To enable the
+in-memory journal you need to pass the following configuration to the @scala[`ScalaTestWithActorTestKit`]@java[`TestKitJunitResource`].
+
+Scala
+:  @@snip [AccountExampleDocSpec.scala](/akka-cluster-sharding-typed/src/test/scala/docs/akka/cluster/sharding/typed/AccountExampleDocSpec.scala) { #inmem-config }
+
+Java
+:  @@snip [AccountExampleDocTest.java](/akka-cluster-sharding-typed/src/test/java/jdocs/akka/cluster/sharding/typed/AccountExampleDocTest.java) { #inmem-config } 
+
+Optionally you can also configure a snapshot store. To enable the file based snapshot store you need to pass the
+following configuration to the @scala[`ScalaTestWithActorTestKit`]@java[`TestKitJunitResource`].
+
+Scala
+:  @@snip [AccountExampleDocSpec.scala](/akka-cluster-sharding-typed/src/test/scala/docs/akka/cluster/sharding/typed/AccountExampleDocSpec.scala) { #snapshot-store-config }
+
+Java
+:  @@snip [AccountExampleDocTest.java](/akka-cluster-sharding-typed/src/test/java/jdocs/akka/cluster/sharding/typed/AccountExampleDocTest.java) { #snapshot-store-config }
+
+Then you can `spawn` the `EventSourcedBehavior` and verify the outcome of sending commands to the actor using
+the facilities of the @ref:[ActorTestKit](testing-async.md).
+
+A full test for the `AccountEntity`, which is shown in the @ref:[Style Guide](style-guide.md), may look like this:
+
+Scala
+:  @@snip [AccountExampleDocSpec.scala](/akka-cluster-sharding-typed/src/test/scala/docs/akka/cluster/sharding/typed/AccountExampleDocSpec.scala) { #test }
+
+Java
+:  @@snip [AccountExampleDocTest.java](/akka-cluster-sharding-typed/src/test/java/jdocs/akka/cluster/sharding/typed/AccountExampleDocTest.java) { #test }  
+
+Note that each test case is using a different `PersistenceId` to not interfere with each other.
+
+## Integration testing
+
+The in-memory journal and file based snapshot store can be used also for integration style testing of a single
+`ActorSystem`, for example when using Cluster Sharding with a single Cluster node.
+
+For tests that involve more than one Cluster node you have to use another journal and snapshot store.
+While it's possible to use the @ref:[Persistence Plugin Proxy](../persistence-plugins.md#persistence-plugin-proxy)
+it's often better and more realistic to use a real database.
+
+See [akka-samples issue #128](https://github.com/akka/akka-samples/issues/128).    

akka-docs/src/main/paradox/typed/persistence.md

@@ -7,6 +7,7 @@ project.description: Event Sourcing with Akka Persistence enables actors to pers
 
 * [Persistence coding style](persistence-style.md)
 * [Persistence snapshotting](persistence-snapshot.md)
+* [Persistence testing](persistence-testing.md)
 * [Persistence schema evolution](../persistence-schema-evolution.md)
 * [Persistence query](../persistence-query.md)
 * [Persistence query LevelDB](../persistence-query-leveldb.md)
@@ -23,7 +24,7 @@ For the Akka Classic documentation of this feature see @ref:[Classic Akka Persis
 
 ## Dependency
 
-To use Akka Persistence Typed, add the module to your project:
+To use Akka Persistence, add the module to your project:
 
 @@dependency[sbt,Maven,Gradle] {
   group=com.typesafe.akka

akka-docs/src/main/paradox/typed/testing.md

@@ -8,7 +8,7 @@ For the Akka Classic documentation of this feature see @ref:[Classic Testing](..
 
 ## Dependency
 
-To use Akka TestKit add the module to your project:
+To use Actor TestKit add the module to your project:
 
 @@dependency[sbt,Maven,Gradle] {
   group=com.typesafe.akka