MinimalPipelineTest.scala

import org.apache.beam.sdk.testing.{NeedsRunner, PAssert, TestPipeline}
import org.apache.beam.sdk.transforms.DoFn.ProcessElement
import org.apache.beam.sdk.transforms.{Create, DoFn, ParDo}
import org.junit.experimental.categories.Category
import org.junit.{Rule, Test}
import org.scalatest.junit.JUnitSuite

import scala.annotation.meta.getter
import scala.collection.JavaConverters._

class TimesTwoDoFn extends DoFn[Int, Int] {
  @ProcessElement
  def processElement(c: ProcessContext): Unit = {
    c.output(c.element * 2)
  }
}

class TimesFiveDoFn extends DoFn[Int, Int] {
  @ProcessElement
  def processElement(c: ProcessContext): Unit = {
    c.output(c.element * 5)
  }
}

class MinimalPipelineTest extends JUnitSuite {

  @(Rule@getter) // The @Rule 'pipeline' must be public.
  val pipeline: TestPipeline = TestPipeline.create()

  @Test
  @Category(Array(classOf[NeedsRunner]))
  def myTimesTenPipelineTest(): Unit = {
    val input = Iterable(1, 2, 3).asJava

    val actualOutput = pipeline.apply(Create.of(input))
      .apply("x2", ParDo.of(new TimesTwoDoFn()))
      .apply("x5", ParDo.of(new TimesFiveDoFn()))

    val expectedOutput = Iterable(10, 20, 30).asJava

    PAssert that actualOutput containsInAnyOrder expectedOutput

    pipeline.run().waitUntilFinish()
  }

}

For testing the whole pipeline ensure the following in build.sbt:

 "junit" % "junit" % "4.12" % Test,
  "org.hamcrest" % "hamcrest-all" % "1.3" % Test,