Add hermetic coverage for service boundaries

crates/remora-runtime/src/lib.rs

@@ -332,6 +332,38 @@ fn random_hex<const N: usize>() -> String {
 #[cfg(test)]
 mod tests {
     use super::*;
+    use actix_web::{http::StatusCode, test as actix_test};
+
+    #[actix_web::test]
+    async fn trace_header() {
+        let app = actix_test::init_service(
+            App::new()
+                .wrap(from_fn(trace_request))
+                .route("/", web::get().to(live)),
+        )
+        .await;
+        let trace_id = "4bf92f3577b34da6a3ce929d0e0e4736";
+        let request = actix_test::TestRequest::get()
+            .uri("/")
+            .insert_header(("traceparent", format!("00-{trace_id}-00f067aa0ba902b7-01")))
+            .to_request();
+        let response = actix_test::call_service(&app, request).await;
+
+        assert_eq!(response.status(), StatusCode::OK);
+        let trace = response
+            .headers()
+            .get("traceparent")
+            .unwrap()
+            .to_str()
+            .unwrap();
+        assert!(trace.starts_with(&format!("00-{trace_id}-")));
+        assert!(trace.ends_with("-01"));
+        assert_eq!(trace.len(), 55);
+        assert_eq!(
+            actix_test::read_body(response).await,
+            r#"{"status":"live"}"#
+        );
+    }
 
     #[test]
     fn escapes_prometheus_labels() {