title: java.lang.IncompatibleClassChangeError: Implementing class with ScalaCheck and ScalaTest
body: <p>I'm facing a nasty exception when trying to write a test using ScalaCheck and ScalaTest. Here's my dependencies:</p>
  
  <pre><code>libraryDependencies ++= Seq(
    "org.scalatest" %% "scalatest" % "2.2.6" % "test",
    "org.scalacheck" %% "scalacheck" % "1.13.0" % "test"
  ) 
  </code></pre>
  
  <p>Here's my test:</p>
  
  <pre><code>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]) =&gt; a.size + b.size == (a ::: b).size)
    }
  }
  </code></pre>
  
  <p>When I try to run this I'm getting:</p>
  
  <pre><code>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)
       ...
  </code></pre>
  
  <p>What am I missing here?</p>