Strange exception in SBT test - scala

Question

I am facing an issue with SBT (version 0.13.9). One of my ScalaTest tests fails not deterministic with EOFException.
Stack trace:
Exception in thread "Thread-155" Exception in thread "Thread-159" java.io.EOFException
at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2601)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1319)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
at sbt.React.react(ForkTests.scala:114)
at sbt.ForkTests$$anonfun$mainTestTask$1$Acceptor$2$.run(ForkTests.scala:74)
at java.lang.Thread.run(Thread.java:745)
java.io.EOFException
at java.io.ObjectInputStream$BlockDataInputStream.peekByte(ObjectInputStream.java:2601)
at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1319)
at java.io.ObjectInputStream.readObject(ObjectInputStream.java:371)
at org.scalatest.tools.Framework$ScalaTestRunner$Skeleton$1$React.react(Framework.scala:953)
at org.scalatest.tools.Framework$ScalaTestRunner$Skeleton$1.run(Framework.scala:942)
at java.lang.Thread.run(Thread.java:745)
sbt.ForkMain 59974 failed with exit code 134
I don't see any JVM logs or thread dumps.

Answer 1

Almost certainly this is related to the Java classpath being too long when invoking sbt.ForkMain in certain linux distros. To avoid this I added
javaOptions in Test ++= Seq("-Xms1G","-XX:+CMSClassUnloadingEnabled","-XX:+UseConcMarkSweepGC")
to the build.sbt file. I reckon CMSClassUnloadingEnabled is where the magic happens.

Answer 2

SBT single thread or multi threaded tests forks the JVM and if the host name is not resolved it just fails with this error message. If you look at the logs in the tests, you might see
Uncaught exception when running tests: java.net.ConnectException: Operation timed out
So the easy way to resolve this is to add your hostname to the /etc/hosts and map it to localhost something like this
::1 localhost blahblah
This should resolve the issue.