Poll example

src/error.rs

@@ -5,7 +5,7 @@
 ///
 /// In many systems there can be a single function for handling any critical error as a critical
 /// error always means everything needs to be stopped.
-#[derive(Copy, Clone, Eq, PartialEq)]
+#[derive(Copy, Clone, Eq, PartialEq, Debug)]
 pub enum CriticalError {
     /// Critical communication failed and retries are either impossible or also failed.
     Communication,