Multi JVM Testing

Supports running applications (objects with main methods) and ScalaTest tests in multiple JVMs at the same time. Useful for integration testing where multiple systems communicate with each other.

Setup

The multi-JVM testing is an sbt plugin that you can find at https://github.com/sbt/sbt-multi-jvm. To configure it in your project you should do the following steps:

1. Add it as a plugin by adding the following to your project/plugins.sbt:

   addSbtPlugin("com.github.sbt" % "sbt-multi-jvm" % "0.6.0")
   

2. Add multi-JVM testing to build.sbt or project/Build.scala by enabling MultiJvmPlugin and setting the MultiJvm config.

   ```none
   lazy val root = (project in file("."))
     .enablePlugins(MultiJvmPlugin)
     .configs(MultiJvm)
   ```
   

Please note that by default MultiJvm test sources are located in src/multi-jvm/..., and not in src/test/....

Running tests

The multi-JVM tasks are similar to the normal tasks: test, testOnly, and run, but are under the multi-jvm configuration.

So in Akka, to run all the multi-JVM tests in the akka-remote project use (at the sbt prompt):

akka-remote-tests/multi-jvm:test

Or one can change to the akka-remote-tests project first, and then run the tests:

project akka-remote-tests
multi-jvm:test

To run individual tests use testOnly:

multi-jvm:testOnly akka.remote.RandomRoutedRemoteActor

More than one test name can be listed to run multiple specific tests. Tab-completion in sbt makes it easy to complete the test names.

It’s also possible to specify JVM options with testOnly by including those options after the test names and --. For example:

multi-jvm:testOnly akka.remote.RandomRoutedRemoteActor -- -Dsome.option=something

Creating application tests

The tests are discovered, and combined, through a naming convention. MultiJvm test sources are located in src/multi-jvm/.... A test is named with the following pattern:

{TestName}MultiJvm{NodeName}

That is, each test has MultiJvm in the middle of its name. The part before it groups together tests/applications under a single TestName that will run together. The part after, the NodeName, is a distinguishing name for each forked JVM.

So to create a 3-node test called Sample, you can create three applications like the following:

package sample

object SampleMultiJvmNode1 {
  def main(args: Array[String]) {
    println("Hello from node 1")
  }
}

object SampleMultiJvmNode2 {
  def main(args: Array[String]) {
    println("Hello from node 2")
  }
}

object SampleMultiJvmNode3 {
  def main(args: Array[String]) {
    println("Hello from node 3")
  }
}

When you call multi-jvm:run sample.Sample at the sbt prompt, three JVMs will be spawned, one for each node. It will look like this:

> multi-jvm:run sample.Sample
...
[info] * sample.Sample
[JVM-1] Hello from node 1
[JVM-2] Hello from node 2
[JVM-3] Hello from node 3
[success] Total time: ...

Changing Defaults

You can specify JVM options for the forked JVMs:

jvmOptions in MultiJvm := Seq("-Xmx256M")

You can change the name of the multi-JVM test source directory by adding the following configuration to your project:

unmanagedSourceDirectories in MultiJvm :=
   Seq(baseDirectory(_ / "src/some_directory_here")).join.value

You can change what the MultiJvm identifier is. For example, to change it to ClusterTest use the multiJvmMarker setting:

multiJvmMarker in MultiJvm := "ClusterTest"

Your tests should now be named {TestName}ClusterTest{NodeName}.

Configuration of the JVM instances

You can define specific JVM options for each of the spawned JVMs. You do that by creating a file named after the node in the test with suffix .opts and put them in the same directory as the test.

For example, to feed the JVM options -Dakka.remote.port=9991 and -Xmx256m to the SampleMultiJvmNode1 let’s create three *.opts files and add the options to them. Separate multiple options with space.

SampleMultiJvmNode1.opts:

-Dakka.remote.port=9991 -Xmx256m

SampleMultiJvmNode2.opts:

-Dakka.remote.port=9992 -Xmx256m

SampleMultiJvmNode3.opts:

-Dakka.remote.port=9993 -Xmx256m

ScalaTest

There is also support for creating ScalaTest tests rather than applications. To do this use the same naming convention as above, but create ScalaTest suites rather than objects with main methods. You need to have ScalaTest on the classpath. Here is a similar example to the one above but using ScalaTest:

package sample

import org.scalatest.wordspec.AnyWordSpec
import org.scalatest.matchers.must.Matchers

class SpecMultiJvmNode1 extends AnyWordSpec with Matchers {
  "A node" should {
    "be able to say hello" in {
      val message = "Hello from node 1"
      message must be("Hello from node 1")
    }
  }
}

class SpecMultiJvmNode2 extends AnyWordSpec with Matchers {
  "A node" should {
    "be able to say hello" in {
      val message = "Hello from node 2"
      message must be("Hello from node 2")
    }
  }
}

To run just these tests you would call multi-jvm:testOnly sample.Spec at the sbt prompt.

Multi Node Additions

There has also been some additions made to the SbtMultiJvm plugin to accommodate the may change module multi node testing, described in that section.

Example project

Akka Cluster Sample with Scala is an example project that can be downloaded, and with instructions of how to run.

This project illustrates Cluster features and also includes Multi JVM Testing with the sbt-multi-jvm plugin.