Fix warnings_checker.dart handling of multitests

tests/language/constructor_initializer_test.dart

Index: tests/language/constructor_initializer_test.dart
diff --git a/tests/language/constructor_initializer_test.dart b/tests/language/constructor_initializer_test.dart
index a4dec3f107d48fa422e8c588a75a26e826ab2882..cae3ca1028c940233780b6fb845dc62a307932cb 100644
--- a/tests/language/constructor_initializer_test.dart
+++ b/tests/language/constructor_initializer_test.dart
@@ -11,7 +11,7 @@ class A {
     // is remembered in the constructor body.
     Expect.equals(x, _x + 1);
     Expect.equals(y, _y + 1);
-    Expect.isFalse(?y); // /// 01: compile-time error
+    Expect.isFalse(?y); // //# 01: compile-time error
   }
 }