Add test of scan error

tests/test_error.rs

@@ -3,7 +3,7 @@
 use indoc::indoc;
 use serde::de::{Deserialize, SeqAccess, Visitor};
 use serde_derive::{Deserialize, Serialize};
-use serde_yaml::Deserializer;
+use serde_yaml::{Deserializer, Value};
 use std::collections::BTreeMap;
 use std::fmt::{self, Debug};
 
@@ -15,6 +15,13 @@ where
     assert_eq!(expected, result.unwrap_err().to_string());
 }
 
+#[test]
+fn test_scan_error() {
+    let yaml = ">\n@";
+    let expected = "deserializing from YAML containing more than one document is not supported";
+    test_error::<Value>(yaml, expected);
+}
+
 #[test]
 fn test_incorrect_type() {
     let yaml = indoc! {"