Add test case to invalidate & String::operator = (const char *cstr)

Author: giulcioffi

Diff for: test/src/String/test_operators.cpp

@@ -136,4 +136,12 @@ TEST_CASE ("Testing & String::operator = (const String &)", "[String-operator+-1
   arduino::String str = (str1+ch);
   REQUIRE(str.compareTo("Hello!") == 0);
   */
+}
+
+TEST_CASE ("Testing & String::operator = (const char *)", "[String-operator+-14]")
+{
+  char *buffer = NULL;
+  arduino::String str("Hello");
+  str = buffer;
+  REQUIRE(str.compareTo("Hello") == 0);
 }