Add pickup-drop test and fix hand state handling (#15212)

Content.Client/Hands/Systems/HandsSystem.cs

@@ -72,11 +72,13 @@ namespace Content.Client.Hands.Systems
                 List<Hand> addedHands = new();
                 foreach (var hand in state.Hands)
                 {
-                    if (component.Hands.TryAdd(hand.Name, hand))
-                    {
-                        hand.Container = _containerSystem.EnsureContainer<ContainerSlot>(uid, hand.Name, manager);
-                        addedHands.Add(hand);
-                    }
+                    if (component.Hands.ContainsKey(hand.Name))
+                        continue;
+
+                    var container = _containerSystem.EnsureContainer<ContainerSlot>(uid, hand.Name, manager);
+                    var newHand = new Hand(hand.Name, hand.Location, container);
+                    component.Hands.Add(hand.Name, newHand);
+                    addedHands.Add(newHand);
                 }
 
                 foreach (var name in component.Hands.Keys)

Content.IntegrationTests/Tests/Hands/HandTests.cs

@@ -0,0 +1,56 @@
+using System.Linq;
+using System.Threading.Tasks;
+using Content.Shared.Hands.Components;
+using Content.Shared.Hands.EntitySystems;
+using NUnit.Framework;
+using Robust.Server.Player;
+using Robust.Shared.GameObjects;
+using Robust.Shared.Map;
+
+namespace Content.IntegrationTests.Tests.Hands;
+
+[TestFixture]
+public sealed class HandTests
+{
+    [Test]
+    public async Task TestPickupDrop()
+    {
+        await using var pairTracker = await PoolManager.GetServerClient();
+        var server = pairTracker.Pair.Server;
+
+        var entMan = server.ResolveDependency<IEntityManager>();
+        var playerMan = server.ResolveDependency<IPlayerManager>();
+        var mapMan = server.ResolveDependency<IMapManager>();
+        var sys = entMan.System<SharedHandsSystem>();
+
+        var data = await PoolManager.CreateTestMap(pairTracker);
+        await PoolManager.RunTicksSync(pairTracker.Pair, 5);
+
+        EntityUid item = default;
+        EntityUid player = default;
+        HandsComponent hands = default!;
+        await server.WaitPost(() =>
+        {
+            player = playerMan.Sessions.First().AttachedEntity!.Value;
+            var xform = entMan.GetComponent<TransformComponent>(player);
+            item = entMan.SpawnEntity("Crowbar", xform.MapPosition);
+            hands = entMan.GetComponent<HandsComponent>(player);
+            sys.TryPickup(player, item, hands.ActiveHand!);
+        });
+
+        // run ticks here is important, as errors may happen within the container system's frame update methods.
+        await PoolManager.RunTicksSync(pairTracker.Pair, 5);
+        Assert.That(hands.ActiveHandEntity == item);
+
+        await server.WaitPost(() =>
+        {
+            sys.TryDrop(player, item, null!);
+        });
+
+        await PoolManager.RunTicksSync(pairTracker.Pair, 5);
+        Assert.That(hands.ActiveHandEntity == null);
+
+        await server.WaitPost(() => mapMan.DeleteMap(data.MapId));
+        await pairTracker.CleanReturnAsync();
+    }
+}