$ cat > test.scala <<EOF
package myPackage {
  private[myPackage] class Test
  object A extends Test
}
EOF

 $ scalac test.scala
 $ cat > test.scala <<EOF
package myPackage {
  private class Test
  object A extends Test
}
EOF
 $ scalac test.scala
test.scala:3: error: private class Test escapes its defining scope as part of type myPackage.Test
  object A extends Test
                   ^
one error found