Expected frames allow the user to specify a list of frames that the h3i client expects to receive over a given connection.

If h3i sees all of the exected frames over the course of the connection, it will pre-emptively close the connection with a CONNECTION_CLOSE frame. If h3i does not see all of the expected frames, the resulting ConnectionSummary will contain a list of the missing target frames for future inspection.

This gives users a way to close tests out without waiting for the idle timeout, or adding Wait/ConnectionClose actions to the end of each test. This should vastly speed up test suites that have a large number of h3i tests.

In the absence of full-fledged integration tests, I modified the content_length_mismatch example to expect a 400, and remove the existing Wait/CC actions:

-        Action::Wait {
-            wait_type: WaitType::StreamEvent(StreamEvent {
-                stream_id: STREAM_ID,
-                event_type: StreamEventType::Headers,
-            }),
-        },
-        Action::ConnectionClose {
-            error: quiche::ConnectionError {
-                is_app: true,
-                error_code: quiche::h3::WireErrorCode::NoError as u64,
-                reason: vec![],
-            },
-        },
     ];
 
-    let summary =
-        sync_client::connect(config, &actions, None).expect("connection failed");
+    let summary = sync_client::connect(
+        config,
+        &actions,
+        Some(vec![ExpectedFrame::new(
+            0,
+            vec![quiche::h3::Header::new(b":status", b"400")].into(),
+        )]),
+    )
+    .expect("connection failed");

Taking a PCAP:

You can see that the client instantly sends the CC frame upon receiving the headers frame, without us needing to specify the action.