test(e2e): a room announces members arriving and leaving

UserJoinedRoom and UserLeftRoom (codes 16 and 17) were parsed and applied
to the roster with nothing proving either end of that, which is the kind
of gap that only shows up when someone relies on it.

soulseek-rs-lib/tests/e2e.rs

@@ -5212,3 +5212,75 @@ fn a_peer_tells_us_about_itself_when_asked() {
 
     let _ = std::fs::remove_dir_all(share_dir);
 }
+
+#[test]
+fn a_room_reports_members_arriving_and_leaving() {
+    use soulseek_rs::types::RoomEvent;
+    let server = server_or_skip!();
+
+    let room = "e2e_room_comings";
+    let mut alice =
+        Client::with_settings(server.settings("e2e_comings_alice", "pw"));
+    alice.connect().expect("alice connect");
+    assert!(alice.login().expect("alice login"));
+    alice.join_room(room).expect("alice joins");
+    std::thread::sleep(Duration::from_millis(500));
+    let _ = alice.take_room_events();
+
+    // Bob arrives after her: she is told (code 16), and her roster grows.
+    let mut bob =
+        Client::with_settings(server.settings("e2e_comings_bob", "pw"));
+    bob.connect().expect("bob connect");
+    assert!(bob.login().expect("bob login"));
+    bob.join_room(room).expect("bob joins");
+
+    let joined =
+        await_room_event(&alice, Duration::from_secs(5), |event| match event {
+            RoomEvent::UserJoined { room: r, username }
+                if r == room && username == "e2e_comings_bob" =>
+            {
+                Some(())
+            }
+            _ => None,
+        });
+    assert!(joined.is_some(), "alice should be told bob arrived");
+    assert!(
+        alice
+            .room_members(room)
+            .iter()
+            .any(|u| u == "e2e_comings_bob"),
+        "the roster should carry bob, got {:?}",
+        alice.room_members(room)
+    );
+
+    // And when he leaves (code 17) the roster loses him again.
+    bob.leave_room(room).expect("bob leaves");
+    let left =
+        await_room_event(&alice, Duration::from_secs(5), |event| match event {
+            RoomEvent::UserLeft { room: r, username }
+                if r == room && username == "e2e_comings_bob" =>
+            {
+                Some(())
+            }
+            _ => None,
+        });
+    assert!(left.is_some(), "alice should be told bob left");
+
+    let deadline = Instant::now() + Duration::from_secs(3);
+    while Instant::now() < deadline
+        && alice
+            .room_members(room)
+            .iter()
+            .any(|u| u == "e2e_comings_bob")
+    {
+        std::thread::sleep(Duration::from_millis(100));
+    }
+    assert!(
+        !alice
+            .room_members(room)
+            .iter()
+            .any(|u| u == "e2e_comings_bob"),
+        "the roster should drop him, got {:?}",
+        alice.room_members(room)
+    );
+}