优化了平衡，尤其对于向后倾倒的几种极限情况进行优化

Shibo-main-TOMMY/lib/ArduinoJson/extras/tests/JsonObject/iterator.cpp

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+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2023, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+using namespace Catch::Matchers;
+
+TEST_CASE("JsonObject::begin()/end()") {
+  StaticJsonDocument<JSON_OBJECT_SIZE(2)> doc;
+  JsonObject obj = doc.to<JsonObject>();
+  obj["ab"] = 12;
+  obj["cd"] = 34;
+
+  SECTION("NonConstIterator") {
+    JsonObject::iterator it = obj.begin();
+    REQUIRE(obj.end() != it);
+    REQUIRE(it->key() == "ab");
+    REQUIRE(12 == it->value());
+    ++it;
+    REQUIRE(obj.end() != it);
+    REQUIRE(it->key() == "cd");
+    REQUIRE(34 == it->value());
+    ++it;
+    REQUIRE(obj.end() == it);
+  }
+
+  SECTION("Dereferencing end() is safe") {
+    REQUIRE(obj.end()->key().isNull());
+    REQUIRE(obj.end()->value().isNull());
+  }
+
+  SECTION("null JsonObject") {
+    JsonObject null;
+    REQUIRE(null.begin() == null.end());
+  }
+}
+
+TEST_CASE("JsonObjectConst::begin()/end()") {
+  StaticJsonDocument<JSON_OBJECT_SIZE(2)> doc;
+  JsonObject obj = doc.to<JsonObject>();
+  obj["ab"] = 12;
+  obj["cd"] = 34;
+
+  JsonObjectConst cobj = obj;
+
+  SECTION("Iteration") {
+    JsonObjectConst::iterator it = cobj.begin();
+    REQUIRE(cobj.end() != it);
+    REQUIRE(it->key() == "ab");
+    REQUIRE(12 == it->value());
+
+    ++it;
+    REQUIRE(cobj.end() != it);
+    JsonPairConst pair = *it;
+    REQUIRE(pair.key() == "cd");
+    REQUIRE(34 == pair.value());
+
+    ++it;
+    REQUIRE(cobj.end() == it);
+  }
+
+  SECTION("Dereferencing end() is safe") {
+    REQUIRE(cobj.end()->key().isNull());
+    REQUIRE(cobj.end()->value().isNull());
+  }
+
+  SECTION("null JsonObjectConst") {
+    JsonObjectConst null;
+    REQUIRE(null.begin() == null.end());
+  }
+}