Add test for enodev errors

tests/enodev.rs

@@ -0,0 +1,33 @@
+#[cfg(target_os = "linux")]
+use wireguard_uapi::set;
+#[cfg(target_os = "linux")]
+use wireguard_uapi::WgSocket;
+
+#[cfg(target_os = "linux")]
+#[test]
+// WireGuard returns an ENODEV (no device error) when you attempt to update a
+// WireGuard device that hasn't been created yet.
+//
+// Instead of properly reporting this error, the library currently swallows it
+// and reports "No ack received". Adding this test now to record what currently
+// happens and comment on the ideal future state.
+//
+// See https://github.com/gluxon/wireguard-uapi-rs/issues/28
+fn missing_device_returns_sensible_error() -> anyhow::Result<()> {
+    let mut wg = WgSocket::connect()?;
+    let ifname = "wg404";
+
+    let set_device_args = set::Device::from_ifname(ifname)
+        .flags(vec![set::WgDeviceF::ReplacePeers])
+        .peers(vec![]);
+    let set_device_result = wg.set_device(set_device_args);
+
+    let existing_err_message = set_device_result.unwrap_err().to_string();
+
+    // TODO: Ensure this library returns more sensible errors. Update the "No
+    // ack received" string below to "No device found by interface name or
+    // public key".
+    assert_eq!(existing_err_message, "No ack received");
+
+    Ok(())
+}