Prevent overwriting existing documents.

src/lib.rs

@@ -22,6 +22,7 @@ pub enum ActionType {
 
 #[derive(Clone, Debug)]
 pub enum ErrorType {
+    DocumentAlreadyExists,
     DocumentNotFound,
 }
 
@@ -74,7 +75,8 @@ mod mtt_replies {
         let reply = MTTReply::new(msg);
         match reply.get_error() {
             Some(err) => match err {
-                ErrorType::DocumentNotFound => {}
+                ErrorType::DocumentNotFound => {},
+                _ => unreachable!("got {:?}: should have been document not found", err),
             },
             None => unreachable!("should return an error type"),
         }
@@ -96,6 +98,7 @@ mod mtt_replies {
         match reply.get_error() {
             Some(err) => match err {
                 ErrorType::DocumentNotFound => {}
+                _ => unreachable!("got {:?}: should have been document not found", err),
             },
             None => unreachable!("should return an error type"),
         }