Test ErrorCode handling

Author: tomasol

tests/http_handle_error_code.rs

@@ -0,0 +1,19 @@
+use wstd::http::{Body, Client, Request, error::ErrorCode};
+
+/// Test that `outgoing_handler::handle` errors are properly propagated.
+#[wstd::test]
+async fn handle_returns_error_code() -> Result<(), Box<dyn std::error::Error>> {
+    let request = Request::get("ftp://example.com/")
+        .body(Body::empty())?;
+
+    let result = Client::new().send(request).await;
+
+    assert!(result.is_err(), "request with unsupported scheme should fail");
+    let error = result.unwrap_err();
+    assert!(
+        error.downcast_ref::<ErrorCode>().is_some(),
+        "expected an ErrorCode, got: {error:?}"
+    );
+
+    Ok(())
+}