Add more test

Author: liufengyun

tests/patmat/t11457b.scala

@@ -0,0 +1,24 @@
+sealed trait Command {
+  type Reply
+}
+
+final case class Create() extends Command {
+  type Reply = CreateReply
+  val reply: Reply = CreateReply()
+}
+
+final case class Set() extends Command {
+  type Reply = SetReply
+  val reply: Reply = SetReply()
+}
+
+case class CreateReply()
+case class SetReply()
+
+def process[R](command: Command { type Reply = R }): R =
+  command match {
+    case create: Create => create.reply
+    case set: Set       => set.reply
+//                         ^
+// Warning: unreachable code
+  }