test: add parse line malformed word test

src/parse.rs

@@ -41,4 +41,12 @@ mod tests {
             ))
         )
     }
+
+    #[test]
+    fn test_parse_malformed() {
+        assert_eq!(
+            parse_line("keyword \"malformed"),
+            Err(ShellError::MalformedArgs("keyword \"malformed".to_string()))
+        )
+    }
 }