Increase test coverage for generic modules

src/error.rs

@@ -109,3 +109,25 @@ impl error::Error for OsError {}
 impl error::Error for ExternalError {}
 impl error::Error for NotSupportedError {}
 impl error::Error for RunLoopError {}
+
+#[cfg(test)]
+mod tests {
+    #![allow(clippy::redundant_clone)]
+
+    use super::*;
+
+    // Eat attributes for testing
+    #[test]
+    fn ensure_fmt_does_not_panic() {
+        let _ = format!(
+            "{:?}, {}",
+            NotSupportedError::new(),
+            NotSupportedError::new().clone()
+        );
+        let _ = format!(
+            "{:?}, {}",
+            ExternalError::NotSupported(NotSupportedError::new()),
+            ExternalError::NotSupported(NotSupportedError::new())
+        );
+    }
+}