add classTag test

Author: liufengyun

tests/neg-custom-args/isInstanceOf/classTag.scala

@@ -0,0 +1,13 @@
+import scala.reflect.ClassTag
+
+object IsInstanceOfClassTag {
+  def safeCast[T: ClassTag](x: Any): Option[T] = {
+    x match {
+      case x: T => Some(x)
+      case _ => None
+    }
+  }
+
+  def foo(x: Any): Boolean =
+    x.isInstanceOf[List[String]]  // error
+}