Add test case.

We are still lacking the setup to do this right for mixed Scala 2/Dotty runtime tests. So I checked into `pos` for now.

Author: odersky

tests/pos/scala2traits/dotty-subclass.scala

@@ -0,0 +1,27 @@
+// This is supposed to be compiled by Dotty
+class Sub extends T
+
+class A extends S2T with S2Tprivate {
+  val a: Int = 3
+  var b = 2
+}
+
+object Main {
+  def main(args: Array[String]): Unit = {
+    val sub = new Sub
+    println(sub.d)
+    println(sub.v)
+    println(sub.O)
+    println(sub.w)
+
+    val a = new A
+    a.x += a.y
+    println(a.x)
+    println(a.f(a.a + a.b))
+
+    a.xx += a.yy
+    println(a.x)
+    println(a.ff(a.xx))
+  }
+}
+

tests/pos/scala2traits/scala-trait.scala

@@ -0,0 +1,31 @@
+// This is supposed to be compiled by Scala 2.11
+trait T {
+  def d = 42
+  val v = ""
+  object O
+  final val w = 33
+}
+
+trait S2T {
+  var x: Int = 0
+  lazy val y: Int = 1
+//  val z: Int = 2
+  val a: Int
+  var b: Int
+
+  def f(x: Int): Int = x + y
+}
+
+trait S2Tprivate {
+  private var x: Int = 0
+  private lazy val y: Int = 1
+//  private val z: Int = 2  // @darkdimius uncomment once lazy vals can be inherited.
+
+  private def f(x: Int): Int = x + y
+  def xx = x
+  def xx_=(x: Int) = this.x = x
+  def yy = y
+//  def zz = z
+  def ff(x: Int) = f(x)
+}
+