diff --git a/tests/deser.rs b/tests/deser.rs
index f658797..64a010f 100644
--- a/tests/deser.rs
+++ b/tests/deser.rs
@@ -1,7 +1,8 @@
-#![allow(unused)]
 mod formats;
+use cfgfifo::*;
 use serde::{Deserialize, Serialize};
 use std::collections::BTreeMap;
+use tempfile::Builder;
 
 #[derive(Clone, Debug, Deserialize, PartialEq, Serialize)]
 struct Config {
@@ -133,6 +134,7 @@ struct RonConfig {
 }
 
 impl RonConfig {
+    #[allow(unused)]
     fn get() -> RonConfig {
         RonConfig {
             primitives: Primitives::get(),
@@ -150,6 +152,7 @@ struct RonEnums {
 }
 
 impl RonEnums {
+    #[allow(unused)]
     fn get() -> RonEnums {
         RonEnums {
             color: Color::Green,
@@ -174,3 +177,23 @@ enum RonMessage {
         value: String,
     },
 }
+
+#[test]
+fn load_unknown() {
+    let file = Builder::new().suffix(".unk").tempfile().unwrap();
+    let r = load::<Config, _>(file);
+    let Err(LoadError::Identify(e)) = r else {
+        panic!("load() did not fail with Identify error: {r:?}");
+    };
+    assert_eq!(e, IdentifyError::Unknown(String::from("unk")));
+}
+
+#[test]
+fn dump_unknown() {
+    let file = Builder::new().suffix(".unk").tempfile().unwrap();
+    let r = dump(&file, &Config::get());
+    let Err(DumpError::Identify(e)) = r else {
+        panic!("dump() did not fail with Identify error: {r:?}");
+    };
+    assert_eq!(e, IdentifyError::Unknown(String::from("unk")));
+}
diff --git a/tests/formats/json.rs b/tests/formats/json.rs
index 94efc69..018a406 100644
--- a/tests/formats/json.rs
+++ b/tests/formats/json.rs
@@ -110,3 +110,27 @@ fn dump_to_file() {
     assert_eq!(s, format!("{JSON}\n"));
     assert!(s.ends_with("}\n"));
 }
+
+#[test]
+fn fallback_load() {
+    let mut file = Builder::new().suffix(".unk").tempfile().unwrap();
+    writeln!(file, "{JSON}").unwrap();
+    file.flush().unwrap();
+    file.rewind().unwrap();
+    let cfg = Cfgfifo::new().fallback(Some(Format::Json));
+    let r = cfg.load::<Config, _>(file);
+    assert_eq!(r.unwrap(), Config::get());
+}
+
+#[test]
+fn fallback_dump() {
+    let mut file = Builder::new().suffix(".unk").tempfile().unwrap();
+    let cfg = Cfgfifo::new().fallback(Some(Format::Json));
+    let r = cfg.dump(&file, &Config::get());
+    assert!(r.is_ok());
+    file.flush().unwrap();
+    file.rewind().unwrap();
+    let s = read_to_string(file).unwrap();
+    assert_eq!(s, format!("{JSON}\n"));
+    assert!(s.ends_with("}\n"));
+}