Add test

Author: liufengyun

tests/patmat/i8690b.scala

@@ -0,0 +1,4 @@
+def test[A, B](x: (A, B) | (B, A)) = x match {
+  case (u: A, v: B) => (u, v)
+  case (u: B, v: A) => (v, u)
+}