Add test

Author: noti0na1

tests/warn/i20146.scala

@@ -0,0 +1,7 @@
+//> using options -Wunused:imports
+
+def test(list: List[Int]): Int =
+  import list.{head => first}
+  import list.{length => len} // warn
+  import list.{addString => add} // warn
+  first + list.length