test(client): refactor probes and replies tests into submodules

Split the monolithic `probes_replies.rs` file into logical submodules and expose internal packet processing methods to improve test maintainability and coverage of boundary conditions.

crates/irtt-client/src/client/tests/probes_replies/timeouts.rs

@@ -0,0 +1,161 @@
+use super::*;
+
+#[test]
+fn poll_timeouts_emits_echo_loss() {
+    let params = default_params();
+    let server = silent_open_server(params);
+    let config = ClientConfig {
+        probe_timeout: Duration::from_millis(100),
+        socket_config: crate::SocketConfig {
+            recv_timeout: Some(Duration::from_millis(50)),
+            ..Default::default()
+        },
+        ..default_test_config(server.addr)
+    };
+    let mut client = Client::connect(config).unwrap();
+    assert_open_started(client.open().unwrap());
+
+    client.send_probe().unwrap();
+    client.send_probe().unwrap();
+
+    let no_loss = client.poll_timeouts().unwrap();
+    assert!(no_loss.is_empty());
+
+    thread::sleep(Duration::from_millis(150));
+    let events = client.poll_timeouts().unwrap();
+    assert_eq!(events.len(), 2);
+    for event in &events {
+        assert!(matches!(event, ClientEvent::EchoLoss { .. }));
+    }
+    server.join();
+}
+
+#[test]
+fn late_reply_after_timeout_preserves_measurement_metadata() {
+    let params = default_params();
+    let server = start_fake_server(move |socket, tx| {
+        let (_, peer) = recv_request(&socket, &tx);
+        let reply = open_reply(FLAG_OPEN | FLAG_REPLY, TOKEN, &params, None);
+        socket.send_to(&reply, peer).unwrap();
+
+        let mut buf = [0_u8; 2048];
+        let (size, _) = socket.recv_from(&mut buf).unwrap();
+        tx.send(buf[..size].to_vec()).unwrap();
+        let seq = u32::from_le_bytes(buf[12..16].try_into().unwrap());
+
+        thread::sleep(Duration::from_millis(90));
+        let ts = TimestampFields {
+            recv_wall: Some(1_000_000_000),
+            recv_mono: Some(100_000),
+            send_wall: Some(1_000_100_000),
+            send_mono: Some(200_000),
+            ..Default::default()
+        };
+        let reply_packet = echo_reply_packet(TOKEN, seq, &params, &ts, None);
+        socket.send_to(&reply_packet, peer).unwrap();
+        socket.send_to(&reply_packet, peer).unwrap();
+    });
+    let config = ClientConfig {
+        probe_timeout: Duration::from_millis(40),
+        socket_config: crate::SocketConfig {
+            recv_timeout: Some(Duration::from_millis(200)),
+            ..Default::default()
+        },
+        ..default_test_config(server.addr)
+    };
+    let mut client = Client::connect(config).unwrap();
+    assert_open_started(client.open().unwrap());
+
+    client.send_probe().unwrap();
+    thread::sleep(Duration::from_millis(60));
+    let losses = client.poll_timeouts().unwrap();
+    assert!(matches!(&losses[0], ClientEvent::EchoLoss { seq: 0, .. }));
+
+    let late = client.recv_once().unwrap();
+    match &late[0] {
+        ClientEvent::LateReply {
+            seq,
+            sent_at,
+            rtt,
+            server_timing,
+            one_way,
+            bytes,
+            packet_meta,
+            ..
+        } => {
+            assert_eq!(*seq, 0);
+            assert!(sent_at.is_some());
+            assert!(rtt.is_some());
+            assert!(server_timing.is_some());
+            assert!(one_way.is_some());
+            assert_eq!(*bytes, echo_packet_len(false, &default_params()));
+            let _ = packet_meta;
+            #[cfg(not(all(target_os = "linux", feature = "ancillary")))]
+            assert_packet_meta_unavailable(packet_meta);
+        }
+        other => panic!("expected stats-eligible LateReply, got {other:?}"),
+    }
+    let duplicate = client.recv_once().unwrap();
+    assert!(matches!(
+        &duplicate[0],
+        ClientEvent::DuplicateReply {
+            seq: 0,
+            bytes,
+            ..
+        } if *bytes == echo_packet_len(false, &default_params())
+    ));
+
+    client.close().unwrap();
+    server.join();
+}
+
+#[test]
+fn pending_full_does_not_send_packet() {
+    let params = Params {
+        duration_ns: 60_000_000_000,
+        ..default_params()
+    };
+    let server = silent_open_server(params);
+    let config = ClientConfig {
+        duration: Some(Duration::from_secs(60)),
+        max_pending_probes: 2,
+        socket_config: crate::SocketConfig {
+            recv_timeout: Some(Duration::from_millis(50)),
+            ..Default::default()
+        },
+        ..default_test_config(server.addr)
+    };
+    let mut client = Client::connect(config).unwrap();
+    assert_open_started(client.open().unwrap());
+
+    client.send_probe().unwrap();
+    client.send_probe().unwrap();
+
+    thread::sleep(Duration::from_millis(30));
+    let before_count: Vec<_> = server.rx.try_iter().collect();
+    let echo_before: Vec<_> = before_count
+        .iter()
+        .filter(|p| p.len() >= 4 && p[3] & FLAG_OPEN == 0 && p[3] & flags::FLAG_CLOSE == 0)
+        .collect();
+    assert_eq!(echo_before.len(), 2);
+
+    assert!(matches!(
+        client.send_probe(),
+        Err(ClientError::PendingLimitExceeded { limit: 2 })
+    ));
+
+    thread::sleep(Duration::from_millis(30));
+    let after: Vec<_> = server.rx.try_iter().collect();
+    let echo_after: Vec<_> = after
+        .iter()
+        .filter(|p| p.len() >= 4 && p[3] & FLAG_OPEN == 0 && p[3] & flags::FLAG_CLOSE == 0)
+        .collect();
+    assert_eq!(
+        echo_after.len(),
+        0,
+        "no packet should be sent when pending is full"
+    );
+
+    client.close().unwrap();
+    server.join();
+}