Added memoryUsage() to JsonArray, JsonObject, and JsonVariant

test/JsonObject/memoryUsage.cpp

@@ -0,0 +1,43 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2018
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+#include <string>
+
+TEST_CASE("JsonObject::memoryUsage()") {
+  DynamicJsonDocument doc(4096);
+  JsonObject obj = doc.to<JsonObject>();
+
+  SECTION("return 0 if uninitialized") {
+    JsonObject unitialized;
+    REQUIRE(unitialized.memoryUsage() == 0);
+  }
+
+  SECTION("JSON_OBJECT_SIZE(0) for empty object") {
+    REQUIRE(obj.memoryUsage() == JSON_OBJECT_SIZE(0));
+  }
+
+  SECTION("JSON_OBJECT_SIZE(1) after add") {
+    obj["hello"] = 42;
+    REQUIRE(obj.memoryUsage() == JSON_OBJECT_SIZE(1));
+  }
+
+  SECTION("includes the size of the key") {
+    obj[std::string("hello")] = 42;
+    REQUIRE(obj.memoryUsage() == JSON_OBJECT_SIZE(1) + 6);
+  }
+
+  SECTION("includes the size of the nested array") {
+    JsonArray nested = obj.createNestedArray("nested");
+    nested.add(42);
+    REQUIRE(obj.memoryUsage() == JSON_OBJECT_SIZE(1) + JSON_ARRAY_SIZE(1));
+  }
+
+  SECTION("includes the size of the nested object") {
+    JsonObject nested = obj.createNestedObject("nested");
+    nested["hello"] = "world";
+    REQUIRE(obj.memoryUsage() == 2 * JSON_OBJECT_SIZE(1));
+  }
+}