Made MTTError a proper Error structure.

src/document/session.rs

@@ -92,7 +92,7 @@ mod sessions {
             field::Field,
         },
         message::wrapper::Records,
-        mtterror::MTTError,
+        mtterror::{ErrorID, MTTError},
         name::{Name, NameType, Names},
         queue::data_director::{Include, Path, RegMsg, Register},
         support_tests::TIMEOUT,
@@ -246,8 +246,8 @@ mod sessions {
         let result = setup.recv().unwrap();
         let action = result.get_action();
         match action {
-            MsgAction::Error(err) => match err {
-                MTTError::FieldDuplicate => {}
+            MsgAction::Error(err) => match err.error_id() {
+                ErrorID::IndexEntryAlreadyExists => {}
                 _ => unreachable!("got {:?}, should have been a field duplicate", err),
             },
             _ => unreachable!("got {:?}, should have been an error", action),