Added tests for FlashStringAdapter

src/ArduinoJson/Strings/IsString.hpp

@@ -0,0 +1,18 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2020
+// MIT License
+
+#pragma once
+
+#include <ArduinoJson/Polyfills/type_traits.hpp>
+
+namespace ARDUINOJSON_NAMESPACE {
+template <typename>
+struct IsString : false_type {};
+
+template <typename T>
+struct IsString<const T> : IsString<T> {};
+
+template <typename T>
+struct IsString<T&> : IsString<T> {};
+}  // namespace ARDUINOJSON_NAMESPACE