Issue 6280 - Check that we don't return invalid entries

test/compiled/StringMap.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #include <string>
 #include "gtest/gtest.h"
 #include "compiled/StringMap.h"
 
 ABP_NS_USING
 
 template<template <typename T> class S>
 void testStringMap()
 {
   S<std::string> map;
+
+  EXPECT_EQ(map.begin(), map.end());
+
   auto key = u"Foobar"_str;
   EXPECT_EQ(key.length(), 6);
   EXPECT_EQ(map.size(), 0);
 
   map[u"Foobar"_str] = "one";
   EXPECT_EQ(map.size(), 1);
+  EXPECT_NE(map.begin(), map.end());
 
   map[u""_str] = "null";
   EXPECT_EQ(map.size(), 2);
 
   auto entry = map.find(u"Foobar"_str);
   EXPECT_TRUE(entry);
 
   entry = map.find(u"Foobar2"_str);
   EXPECT_FALSE(entry);
 
@@ skipping 31 matching lines @@
 
 TEST(TestStringMap, stringMap)
 {
   testStringMap<StringMap>();
 }
 
 TEST(TestStringMap, ownedStringMap)
 {
   testStringMap<OwnedStringMap>();
 }