Added errprs.

src/error.rs

@@ -0,0 +1,51 @@
+use std::{error::Error, fmt};
+
+#[derive(Debug)]
+enum ErrorType {
+    TableAddFieldDuplicate(String),
+}
+
+impl fmt::Display for ErrorType {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            ErrorType::TableAddFieldDuplicate(data) => write!(f, "field '{}' already exists", data),
+        }
+    }
+}
+
+#[derive(Debug)]
+struct MTTError {
+    err: ErrorType,
+}
+
+impl MTTError {
+    fn new(err: ErrorType) -> Self {
+        Self { 
+            err: err,
+        }
+    }
+}
+
+impl Error for MTTError {}
+
+impl fmt::Display for MTTError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.err.to_string())
+    }
+}
+
+#[cfg(test)]
+mod errors {
+    use super::*;
+
+    #[test]
+    fn get_error() {
+        let err = MTTError::new(ErrorType::TableAddFieldDuplicate("tester".to_string()));
+        assert_eq!(err.to_string(), "field 'tester' already exists");
+        assert!(err.source().is_none());
+        let err = MTTError::new(ErrorType::TableAddFieldDuplicate("other".to_string()));
+        assert_eq!(err.to_string(), "field 'other' already exists");
+        assert!(err.source().is_none());
+    }
+}
+