start adding message parser unittests

src/fsfw/cfdp/VarLenFields.h

@@ -74,6 +74,19 @@ struct EntityId : public VarLenField {
   template <typename T>
   explicit EntityId(UnsignedByteField<T> byteField) : VarLenField(byteField) {}
   EntityId(cfdp::WidthInBytes width, size_t entityId) : VarLenField(width, entityId) {}
+
+  ReturnValue_t serializeAsLv(uint8_t **buffer, size_t *size, size_t maxSize) {
+    if (buffer == nullptr or size == nullptr) {
+      return returnvalue::FAILED;
+    }
+    if (*size + 1 + getWidth() > maxSize) {
+      return SerializeIF::BUFFER_TOO_SHORT;
+    }
+    **buffer = getWidth();
+    *buffer += 1;
+    *size += 1;
+    return serialize(buffer, size, maxSize, SerializeIF::Endianness::NETWORK);
+  }
 };
 
 struct TransactionSeqNum : public VarLenField {

src/fsfw/cfdp/tlv/ReservedMessageCreator.cpp

@@ -13,7 +13,7 @@ ReturnValue_t cfdp::ReservedMessageCreator::serialize(
   **buffer = TlvType::MSG_TO_USER;
   *buffer += 1;
   *size += 1;
-  **buffer = getSerializedSize() - 1;
+  **buffer = getSerializedSize() - 2;
   *size += 1;
   *buffer += 1;
   std::memcpy(*buffer, MSG_HEADER, 4);
@@ -23,6 +23,8 @@ ReturnValue_t cfdp::ReservedMessageCreator::serialize(
   *buffer += 1;
   *size += 1;
   std::memcpy(*buffer, msgData, msgSize);
+  *buffer += msgSize;
+  *size += msgSize;
   return returnvalue::OK;
 }