java.lang.IncompatibleClassChangeError: Implementi

Question

I'm facing a nasty exception when trying to write a test using ScalaCheck and ScalaTest. Here's my dependencies:

libraryDependencies ++= Seq(
  "org.scalatest" %% "scalatest" % "2.2.6" % "test",
  "org.scalacheck" %% "scalacheck" % "1.13.0" % "test"
) 

Here's my test:

import org.scalatest.PropSpec
import org.scalatest.prop.Checkers

class MyPropSpec extends PropSpec with Checkers {

  property("List.concat") {
    check((a: List[Int], b: List[Int]) => a.size + b.size == (a ::: b).size)
  }
}

When I try to run this I'm getting:

DeferredAbortedSuite:
 Exception encountered when attempting to run a suite with class name:      org.scalatest.DeferredAbortedSuite *** ABORTED ***
     java.lang.IncompatibleClassChangeError: Implementing class
     at java.lang.ClassLoader.defineClass1(Native Method)
     at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
     at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
     at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
     at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
     at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
     at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
     ...
     java.lang.IncompatibleClassChangeError: Implementing class
     at java.lang.ClassLoader.defineClass1(Native Method)
     at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
     at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:142)
     at java.net.URLClassLoader.defineClass(URLClassLoader.java:467)
     at java.net.URLClassLoader.access$100(URLClassLoader.java:73)
     at java.net.URLClassLoader$1.run(URLClassLoader.java:368)
     at java.net.URLClassLoader$1.run(URLClassLoader.java:362)
     at java.security.AccessController.doPrivileged(Native Method)
     at java.net.URLClassLoader.findClass(URLClassLoader.java:361)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
     at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
     ...

What am I missing here?

Answer 1

ScalaTest 2.2.6 is incompatible with ScalaCheck 1.13.0. Downgrading to "scalacheck" % "1.12.5" helps.

This was reported as https://github.com/rickynils/scalacheck/issues/217. The issue is closed with following resolution:

All current releases of ScalaTest (2.2.6, 3.0.0 etc) are built against ScalaCheck 1.12.1 (see https://github.com/scalatest/scalatest/blob/master/project/scalatest.scala#L134). Therefore, there are no guarantees that you can simply swap out ScalaCheck 1.12.x for 1.13.y. ScalaCheck only maintains binary compatibility within the same minor version series (1.12.1, 1.12.2, 1.12.3 etc).