Add test code for String::substring(...)

Author: giulcioffi

test/CMakeLists.txt

@@ -46,6 +46,7 @@ set(TEST_SRCS
   src/String/test_compareTo.cpp
   src/String/test_comparisonFunc.cpp
   src/String/test_characterAccessFunc.cpp
+  src/String/test_substring.cpp
   src/String/test_indexOf.cpp
   src/String/test_lastIndexOf.cpp
   src/String/test_length.cpp

test/src/String/test_substring.cpp

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2020 Arduino.  All rights reserved.
+ */
+
+/**************************************************************************************
+ * INCLUDE
+ **************************************************************************************/
+
+#include <catch.hpp>
+
+#include <String.h>
+
+/**************************************************************************************
+ * TEST CODE
+ **************************************************************************************/
+
+TEST_CASE ("Testing String::substring(unsigned int, unsigned int)", "[String-substring-01]")
+{
+  WHEN ("left higher than len")
+  {
+    arduino::String str("Hello");
+    str.substring(7,9);
+  }
+
+  WHEN ("right higher than len")
+  {
+    arduino::String str1("Hello");
+    arduino::String str2("ello");
+    REQUIRE(str2.compareTo(str1.substring(1,9)) == 0);
+  }
+
+  WHEN ("left higher than right")
+  {
+    arduino::String str1("Hello");
+    arduino::String str2("ello");
+    REQUIRE(str2.compareTo(str1.substring(9,1)) == 0);
+  }
+}