Adds an integration test for FollowerSystem. (#7048)

Content.IntegrationTests/Tests/FollowerSystemTest.cs

@@ -0,0 +1,63 @@
+using System.Linq;
+using System.Threading.Tasks;
+using Content.Shared.Follower;
+using NUnit.Framework;
+using Robust.Shared.GameObjects;
+using Robust.Shared.IoC;
+using Robust.Shared.Log;
+using Robust.Shared.Map;
+
+namespace Content.IntegrationTests.Tests;
+
+[TestFixture, TestOf(typeof(FollowerSystem))]
+public sealed class FollowerSystemTest : ContentIntegrationTest
+{
+    /// <summary>
+    ///     This test ensures that deleting a map while an entity follows another doesn't throw any exceptions.
+    /// </summary>
+    [Test]
+    public async Task FollowerMapDeleteTest()
+    {
+        var server = StartServerDummyTicker();
+        await server.WaitIdleAsync();
+
+        await server.WaitPost(() =>
+        {
+            var mapMan = IoCManager.Resolve<IMapManager>();
+            var entMan = IoCManager.Resolve<IEntityManager>();
+            var sysMan = IoCManager.Resolve<IEntitySystemManager>();
+            var logger = IoCManager.Resolve<ILogManager>().RootSawmill;
+            var followerSystem = sysMan.GetEntitySystem<FollowerSystem>();
+
+            // Create a map to spawn the observers on.
+            var map = mapMan.CreateMap();
+
+            // Spawn an observer to be followed.
+            var followed = entMan.SpawnEntity("MobObserver", new MapCoordinates(0, 0, map));
+            logger.Info($"Spawned followed observer: {entMan.ToPrettyString(followed)}");
+
+            // Spawn an observer to follow another observer.
+            var follower = entMan.SpawnEntity("MobObserver", new MapCoordinates(0, 0, map));
+            logger.Info($"Spawned follower observer: {entMan.ToPrettyString(follower)}");
+
+            followerSystem.StartFollowingEntity(follower, followed);
+
+            foreach (var ent in entMan.GetEntities().ToArray())
+            {
+                // Let's skip entities that have been deleted, as we want to get their TransformComp for extra info.
+                if (entMan.Deleted(ent))
+                {
+                    logger.Info($"Skipping {entMan.ToPrettyString(ent)}...");
+                    continue;
+                }
+
+                // Log some information about the entity before we delete it.
+                var transform = entMan.GetComponent<TransformComponent>(ent);
+                logger.Info($"Deleting entity {entMan.ToPrettyString(ent)}... Parent: {entMan.ToPrettyString(transform.ParentUid)} | Children: {string.Join(", ", transform.Children.Select(c => entMan.ToPrettyString(c.Owner)))}");
+
+                // Actually delete the entity now.
+                entMan.DeleteEntity(ent);
+            }
+        });
+    }
+}