I am trying to do a very basic serialization of a very simple case class in Scala:

import org.scalatest.wordspec.AnyWordSpecLike
import java.io.{ByteArrayOutputStream, ObjectOutputStream}

class PersistenceSpec extends AnyWordSpecLike{
  case class TestClass(name: String) extends Serializable

  def serializeSomething(): ByteArrayOutputStream = {
    val testItem = TestClass("My Thing")
    val bos: ByteArrayOutputStream = new ByteArrayOutputStream()
    val oos = new ObjectOutputStream(bos)
    oos.writeObject(testItem)
    bos
  }

  "serializeSomething" when {
    "executed" must {
      "successfully serialize" in {
        val outputStream = serializeSomething()
        println(outputStream.toString())
      }
    }
  }
}

When I run this test I get a java.io.NotSerializableException on the call to oos.writeObject(testItem), which makes no sense, since case classes automatically implement Serializable, and this is the simplest possible example.

However, if I paste the code for TestClass and serializeSomething() into repl, I am able to call the function, and it works just fine.

What is different when calling my function via scalatest, vs repl that would cause this exception?

One final note: If I change the call from oos.writeObject(testItem) to oos.writeObject("Hello"), it works fine, even when run from scalatest.

CodePudding user response：

You need to define TestClass outside of PersistenceSpec. Inner class instances automatically get a reference to the instance of the outer class. So, when you write it out, it tries to serialize the PersistenceSpec instance as well, and that of course fails.