Add test case

The first test ensures that the mirror is generated.
The second test will not have mirrors generated.

Author: liufengyun

tests/pos/i10769.scala

@@ -13,9 +13,4 @@ trait STMLike[F[_]] {
     case class Abort(error: Throwable) extends Txn[Nothing]
     case object Noop extends Txn[Nothing]
   }
-
-  class Foo {
-    case class Abort(error: Throwable) extends Txn[Nothing]
-    case object Noop extends Txn[Nothing]
-  }
 }

tests/pos/i10769b.scala

@@ -0,0 +1,21 @@
+package stm
+
+trait STMLike[F[_]] {
+  import Internals._
+
+  sealed abstract class Txn[+A] {}
+
+  object Txn {
+    def abort[A](e: Throwable): Txn[A] = Abort(e)
+  }
+
+  object Internals {
+    case class Abort(error: Throwable) extends Txn[Nothing]
+    case object Noop extends Txn[Nothing]
+  }
+
+  class Foo {
+    case class Abort(error: Throwable) extends Txn[Nothing]
+    case object Noop extends Txn[Nothing]
+  }
+}