sbt - fork in Test

build.sbt

libraryDependencies += "org.scalatest" %% "scalatest" % "3.0.1"
// doesn't work
fork in (Test, test) := true
javaOptions in (Test, test) ++= Seq("-Dkey=value")
// works
fork in Test := true
javaOptions in Test ++= Seq("-Dkey=value")

out

[info] Loading project definition from /home/dos65/projects/try_smth/sbt_1.1.0_RC2/project
[info] Updating ProjectRef(uri("file:/home/dos65/projects/try_smth/sbt_1.1.0_RC2/project/"), "sbt_1-1-0_rc2-build")...
[info] Done updating.
[info] Loading settings from build.sbt ...
[info] Set current project to sbt_1-1-0_rc2 (in build file:/home/dos65/projects/try_smth/sbt_1.1.0_RC2/)
[info] Updating ...
[info] Done updating.
[info] Compiling 1 Scala source to /home/dos65/projects/try_smth/sbt_1.1.0_RC2/target/scala-2.12/classes ...
[info] Done compiling.
[info] Compiling 2 Scala sources to /home/dos65/projects/try_smth/sbt_1.1.0_RC2/target/scala-2.12/test-classes ...
[info] Done compiling.
[info] TestSpec:
[info] TestSpec *** ABORTED ***
[info]   java.lang.RuntimeException: non forked
[info]   at scala.sys.package$.error(package.scala:27)
[info]   at TestSpec.<init>(Test.scala:7)
[info]   at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
[info]   at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
[info]   at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
[info]   at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
[info]   at java.lang.Class.newInstance(Class.java:442)
[info]   at org.scalatest.tools.Framework$ScalaTestTask.execute(Framework.scala:435)
[info]   at sbt.ForkMain$Run$2.call(ForkMain.java:300)
[info]   at sbt.ForkMain$Run$2.call(ForkMain.java:290)
[info]   ...
[info] Run completed in 2 seconds, 944 milliseconds.
[info] Total number of tests run: 0
[info] Suites: completed 0, aborted 1
[info] Tests: succeeded 0, failed 0, canceled 0, ignored 0, pending 0
[info] *** 1 SUITE ABORTED ***
[error] Error during tests:
[error] 	TestSpec
[error] (Test / test) sbt.TestsFailedException: Tests unsuccessful
[error] Total time: 13 s, completed Dec 21, 2017 1:20:32 AM

Test.scala

import org.scalatest._

class TestSpec extends FunSpec {

  sys.props.get("key") match {
    case Some(k) => println(s"ok: $k")
    case None => sys.error("non forked")
  }
  
}