Add interaction tests (#15251)

Content.IntegrationTests/Tests/Interaction/InteractionTestSystem.cs

@@ -0,0 +1,34 @@
+using System.Collections.Generic;
+using Content.Server.Construction;
+using Content.Shared.Construction;
+using Robust.Shared.GameObjects;
+
+namespace Content.IntegrationTests.Tests.Interaction;
+
+/// <summary>
+///     System for listening to events that get raised when construction entities change.
+///     In particular, when construction ghosts become real entities, and when existing entities get replaced with
+///     new ones.
+/// </summary>
+public sealed class InteractionTestSystem : EntitySystem
+{
+    public Dictionary<int, EntityUid> Ghosts = new();
+    public Dictionary<EntityUid, EntityUid> EntChanges = new();
+
+    public override void Initialize()
+    {
+        SubscribeNetworkEvent<AckStructureConstructionMessage>(OnAck);
+        SubscribeLocalEvent<ConstructionChangeEntityEvent>(OnEntChange);
+    }
+
+    private void OnEntChange(ConstructionChangeEntityEvent ev)
+    {
+        EntChanges[ev.Old] = ev.New;
+    }
+
+    private void OnAck(AckStructureConstructionMessage ev)
+    {
+        if (ev.Uid != null)
+            Ghosts[ev.GhostId] = ev.Uid.Value;
+    }
+}