Behold, a unit test for Scanner::BookmarkScope (& scanner bookmarking).

test/cctest/BUILD.gn

 # Copyright 2016 The V8 project authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("../../gni/v8.gni")
 
 v8_executable("cctest") {
   testonly = true
 
   sources = [
@@ skipping 63 matching lines @@
     "interpreter/bytecode-expectations-printer.h",
     "interpreter/interpreter-tester.cc",
     "interpreter/source-position-matcher.cc",
     "interpreter/source-position-matcher.h",
     "interpreter/test-bytecode-generator.cc",
     "interpreter/test-interpreter-intrinsics.cc",
     "interpreter/test-interpreter.cc",
     "interpreter/test-source-positions.cc",
     "libplatform/test-tracing.cc",
     "libsampler/test-sampler.cc",
+    "parsing/test-scanner.cc",
     "print-extension.cc",
     "profiler-extension.cc",
     "test-access-checks.cc",
     "test-accessors.cc",
     "test-api-accessors.cc",
     "test-api-fast-accessor-builder.cc",
     "test-api-interceptors.cc",
     "test-api.cc",
     "test-api.h",
     "test-array-list.cc",
@@ skipping 306 matching lines @@
   if (is_win) {
     # Suppress warnings about importing locally defined symbols.
     if (is_component_build) {
       ldflags = [
         "/ignore:4049",
         "/ignore:4217",
       ]
     }
   }
 }