test: add unit tests for token cache round-trip and edge cases

crates/quicproquo-client/src/client/token_cache.rs

@@ -91,3 +91,88 @@ pub fn clear_cached_session(state_path: &Path) {
     let path = session_cache_path(state_path);
     std::fs::remove_file(&path).ok();
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn plaintext_round_trip() {
+        let dir = tempfile::tempdir().unwrap();
+        let state_path = dir.path().join("state.bin");
+
+        let token = hex::encode(b"session-token-bytes");
+        save_cached_session(&state_path, "alice", &token, None).unwrap();
+        let loaded = load_cached_session(&state_path, None).unwrap();
+        assert_eq!(loaded.username, "alice");
+        assert_eq!(loaded.token_hex, token);
+    }
+
+    #[test]
+    fn encrypted_round_trip() {
+        let dir = tempfile::tempdir().unwrap();
+        let state_path = dir.path().join("state.bin");
+        let password = "strong-password";
+
+        let token = hex::encode(b"encrypted-token");
+        save_cached_session(&state_path, "bob", &token, Some(password)).unwrap();
+
+        // Encrypted file should start with QPCE magic
+        let raw = std::fs::read(session_cache_path(&state_path)).unwrap();
+        assert_eq!(&raw[..4], b"QPCE");
+
+        let loaded = load_cached_session(&state_path, Some(password)).unwrap();
+        assert_eq!(loaded.username, "bob");
+        assert_eq!(loaded.token_hex, token);
+    }
+
+    #[test]
+    fn wrong_password_returns_none() {
+        let dir = tempfile::tempdir().unwrap();
+        let state_path = dir.path().join("state.bin");
+
+        let token = hex::encode(b"secret-token");
+        save_cached_session(&state_path, "carol", &token, Some("correct")).unwrap();
+        let result = load_cached_session(&state_path, Some("wrong"));
+        assert!(result.is_none());
+    }
+
+    #[test]
+    fn missing_file_returns_none() {
+        let dir = tempfile::tempdir().unwrap();
+        let state_path = dir.path().join("nonexistent.bin");
+        assert!(load_cached_session(&state_path, None).is_none());
+    }
+
+    #[test]
+    fn clear_removes_file() {
+        let dir = tempfile::tempdir().unwrap();
+        let state_path = dir.path().join("state.bin");
+
+        let token = hex::encode(b"to-be-deleted");
+        save_cached_session(&state_path, "dave", &token, None).unwrap();
+        assert!(session_cache_path(&state_path).exists());
+
+        clear_cached_session(&state_path);
+        assert!(!session_cache_path(&state_path).exists());
+    }
+
+    #[test]
+    fn malformed_content_returns_none() {
+        let dir = tempfile::tempdir().unwrap();
+        let state_path = dir.path().join("state.bin");
+        let cache_path = session_cache_path(&state_path);
+
+        // Not valid hex on second line
+        std::fs::write(&cache_path, "alice\nnot-hex-data\n").unwrap();
+        assert!(load_cached_session(&state_path, None).is_none());
+
+        // Only one line
+        std::fs::write(&cache_path, "alice\n").unwrap();
+        assert!(load_cached_session(&state_path, None).is_none());
+
+        // Empty file
+        std::fs::write(&cache_path, "").unwrap();
+        assert!(load_cached_session(&state_path, None).is_none());
+    }
+}