Add test for double free (commented) and some documentation.

Author: viferga

source/tests/metacall_test/source/metacall_test.cpp

@@ -292,6 +292,28 @@ TEST_F(metacall_test, DefaultConstructor)
 		};
 
 		EXPECT_EQ((void *)NULL, (void *)metacallfv_s(metacall_function("multiply"), corrupted_args, 2));
+
+		/* Testing freed value input */
+
+		/* TODO: The next snippet of code works but address sanitizer warns about access warning,
+		* because in order to check the magic number we need to access the pointer to the struct.
+		* A better solution would be, when using a custom memory pool allocator (aka object pool)
+		* detect if the pointer is allocated or not in the object pool, so we track it without
+		* need to access the pointer in order to read it. This can be a better improvement but
+		* for now, this would be sufficient to catch most of the errors.
+		*/
+
+		/*
+		void *freed_args[] = {
+			(void *)metacall_value_create_long(3L),
+			(void *)metacall_value_create_long(5L)
+		};
+
+		metacall_value_destroy(freed_args[0]);
+		metacall_value_destroy(freed_args[1]);
+
+		EXPECT_EQ((void *)NULL, (void *)metacallfv_s(metacall_function("multiply"), freed_args, 2));
+		*/
 	}
 #endif /* OPTION_BUILD_LOADERS_PY */