title: Uncaught exception when running tests: java.lang.NoClassDefFoundError: scala/collection/mutable/ArrayOps$ofRef
body: <p>I have a project setup using Intellij Idea scala sbt.</p>
  
  <blockquote>
    <p>sbtVersion = 1.2.8, scalaVersion = 2.13.0</p>
  </blockquote>
  
  <p>I am trying to setup gatling but i get the following errors after i run the command :</p>
  
  <pre><code>gatling: test
  </code></pre>
  
  <blockquote>
    <p>[error] Uncaught exception when running tests:
    java.lang.NoClassDefFoundError:
    scala/collection/mutable/ArrayOps$ofRef [error]
    sbt.ForkMain$ForkError: java.lang.NoClassDefFoundError:
    scala/collection/mutable/ArrayOps$ofRef [error]   at
    io.gatling.sbt.GatlingRunner.tasks(GatlingRunner.scala:31) [error]    at
    sbt.ForkMain$Run.runTests(ForkMain.java:258) [error]  at
    sbt.ForkMain$Run.run(ForkMain.java:144) [error]   at
    sbt.ForkMain$Run.access$100(ForkMain.java:140) [error]    at
    sbt.ForkMain.main(ForkMain.java:126) [error] Caused by:
    sbt.ForkMain$ForkError: java.lang.ClassNotFoundException:
    scala.collection.mutable.ArrayOps$ofRef [error]   at
    java.net.URLClassLoader.findClass(URLClassLoader.java:381) [error]    at
    java.lang.ClassLoader.loadClass(ClassLoader.java:424) [error]     at
    sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) [error]
      at java.lang.ClassLoader.loadClass(ClassLoader.java:357) [error]    at
    io.gatling.sbt.GatlingRunner.tasks(GatlingRunner.scala:31) [error]    at
    sbt.ForkMain$Run.runTests(ForkMain.java:258) [error]  at
    sbt.ForkMain$Run.run(ForkMain.java:144) [error]   at
    sbt.ForkMain$Run.access$100(ForkMain.java:140) [error]    at
    sbt.ForkMain.main(ForkMain.java:126) [info] Simulation(s) execution
    ended. [error] Error during tests: [error]    Forked test harness
    failed: java.io.EOFException [error]  at
    java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2958)
    [error]   at
    java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1538)
    [error]   at
    java.io.ObjectInputStream.readObject(ObjectInputStream.java:431)
    [error]   at sbt.React.react(ForkTests.scala:177) [error]     at
    sbt.ForkTests$Acceptor$2$.run(ForkTests.scala:108) [error]    at
    java.lang.Thread.run(Thread.java:748) [error] (Gatling / test)
    sbt.TestsFailedException: Tests unsuccessful [error] Total time: 6 s,
    completed 29-Aug-2019 09:53:58</p>
  </blockquote>
  
  <p><strong>build.sbt</strong></p>
  
  <pre><code>enablePlugins(GatlingPlugin)
  
  name := "performance-test"
  
  version := "0.1"
  
  scalaVersion := "2.13.0"
  
  scalacOptions := Seq(
    "-encoding", "UTF-8", "-target:jvm-1.8", "-deprecation",
    "-feature", "-unchecked", "-language:implicitConversions", "-language:postfixOps")
  
  libraryDependencies += "io.gatling.highcharts" % "gatling-charts-highcharts" % "3.2.1" % "test,it"
  libraryDependencies += "io.gatling"            % "gatling-test-framework"    % "3.2.1" % "test,it"
  </code></pre>
  
  <p><strong>plugins.sbt</strong></p>
  
  <pre><code>addSbtPlugin("io.gatling" % "gatling-sbt" % "3.0.0")
  </code></pre>
  
  <p><strong>BasicSimulation.scala</strong></p>
  
  <pre><code>package idcheck
  
  import io.gatling.core.Predef._
  import io.gatling.http.Predef._
  import scala.concurrent.duration._
  
  class BasicSimulation extends Simulation {
  
    val httpProtocol = http
      .baseUrl("https://google.com")
  
    val base = scenario("Test")
      .exec(http("base endpoint")
        .get("/"))
  
    setUp(base.inject(atOnceUsers(1)).protocols(httpProtocol))
  
  }
  </code></pre>