Added custom implementation of strtol() (issue #465)

`char` is now treated as an integral type (issue #337, #370)

test/Polyfills_IsInteger_Tests.cpp

@@ -0,0 +1,45 @@
+// Copyright Benoit Blanchon 2014-2017
+// MIT License
+//
+// Arduino JSON library
+// https://github.com/bblanchon/ArduinoJson
+// If you like this project, please add a star!
+
+#include <gtest/gtest.h>
+#include <ArduinoJson/Polyfills/isInteger.hpp>
+
+using namespace ArduinoJson::Polyfills;
+
+struct Polyfills_IsInteger_Tests : testing::Test {
+  void check(bool expected, const char* input) {
+    bool actual = isInteger(input);
+    EXPECT_EQ(expected, actual) << input;
+  }
+};
+#define TEST_(X) TEST_F(Polyfills_IsInteger_Tests, X)
+
+TEST_(Null) {
+  check(false, NULL);
+}
+
+TEST_(FloatNotInteger) {
+  check(false, "3.14");
+  check(false, "-3.14");
+  check(false, "+3.14");
+}
+
+TEST_(Spaces) {
+  check(false, "42 ");
+  check(false, " 42");
+}
+
+TEST_(Valid) {
+  check(true, "42");
+  check(true, "-42");
+  check(true, "+42");
+}
+
+TEST_(ExtraSign) {
+  check(false, "--42");
+  check(false, "++42");
+}