Load dependency class in sbt task

I want to run embedded kafka before all IT test as Tests.Setup from scala object.

So, I have something like

Test / testOptions += Tests.Setup { loader => 
  loader.loadClass("io.github.embeddedkafka.schemaregistry.EmbeddedKafka$").getMethod("start").invoke(null)

The problem is that it can't be found. I've checked loader.getDefinedPackages and there is no classes from io.github. How can I access class from dependency?

If you don't fork (fork := false), when you add a dependency like

libraryDependencies += "io.github.embeddedkafka" %% "embedded-kafka" % "3.7.0" % Test

to (ordinary) build.sbt and run tests like sbt test, then the code similar to yours in build.sbt should work

Test / testOptions += Tests.Setup { loader => 
  val cls = loader.loadClass("io.github.embeddedkafka.EmbeddedKafka$")
  val paramCls = loader.loadClass("io.github.embeddedkafka.EmbeddedKafkaConfig")
  val inst = cls.getField("MODULE$").get(null)
  cls.getDeclaredMethod("start", paramCls).invoke(inst)
}

---

If you fork (fork := true), then indeed, loader.loadClass... won't work

Note: When forking, the ClassLoader containing the test classes cannot be provided because it is in another JVM. Only use the () => Unit variants in this case.

https://www.scala-sbt.org/1.x/docs/Testing.html#Setup+and+Cleanup

You can add to project/build.sbt

libraryDependencies += "io.get-coursier" %% "coursier" % "2.1.9"

and create necessary class loader manually writing in ordinary build.sbt

Test / testOptions += Tests.Setup { loader =>

  import coursier._

  val files = Fetch()
    .addDependencies(
      dep"io.github.embeddedkafka:embedded-kafka_2.12:3.7.0"
    )
    .run()

  val classLoader = new java.net.URLClassLoader(
    files.map(_.toURI.toURL).toArray,
    loader/*getClass.getClassLoader*//*null*/
  )

  val cls = classLoader.loadClass("io.github.embeddedkafka.EmbeddedKafka$")
  val paramCls = classLoader.loadClass("io.github.embeddedkafka.EmbeddedKafkaConfig")
  val inst = cls.getField("MODULE$").get(null)
  cls.getDeclaredMethod("start", paramCls).invoke(inst)
}

https://get-coursier.io/docs/api#fetch-api

---

By the way, you can try to make call directly rather than using reflection

Test / testOptions += Tests.Setup { () => 
  _root_.io.github.embeddedkafka.EmbeddedKafka.start()
}

In such case

libraryDependencies += "io.github.embeddedkafka" %% "embedded-kafka" % "3.7.0" exclude ("com.github.luben", "zstd-jni")

should be added to project/build.sbt.