   .code {
   var s = "abc"
   var i = s.startIndex
-  ++i
-  --i
+  i = i.successor()
+  i = i.predecessor()
   expectCrashLater()
-  --i
+  i = i.predecessor()
 }
 
 StringTraps.test("endIndex/successor")

  .code {
  var s = "abc"
  var i = s.utf8.startIndex
  ++i
  ++i
  ++i
  expectCrashLater()
  s.utf8[i]
}

  .code {
  var s = "abc"
  var i = s.utf16.startIndex
  i = i.successor()
  i = i.successor()
  i = i.successor()
  expectCrashLater()
  s.utf16[i]
}
