Add generic event listener for integration tests (#40367)

* Add generic event listener for integration tests

* cleanup

* assert that the entity has the component

* comments & new overload

Content.IntegrationTests/Tests/Movement/SlippingTest.cs

@@ -1,10 +1,8 @@
 #nullable enable
-using System.Collections.Generic;
-using Content.IntegrationTests.Tests.Interaction;
+using Content.IntegrationTests.Tests.Helpers;
 using Content.Shared.Movement.Components;
 using Content.Shared.Slippery;
 using Content.Shared.Stunnable;
-using Robust.Shared.GameObjects;
 using Robust.Shared.Input;
 using Robust.Shared.Maths;
 
@@ -12,44 +10,32 @@ namespace Content.IntegrationTests.Tests.Movement;
 
 public sealed class SlippingTest : MovementTest
 {
-    public sealed class SlipTestSystem : EntitySystem
-    {
-        public HashSet<EntityUid> Slipped = new();
-        public override void Initialize()
-        {
-            SubscribeLocalEvent<SlipperyComponent, SlipEvent>(OnSlip);
-        }
-
-        private void OnSlip(EntityUid uid, SlipperyComponent component, ref SlipEvent args)
-        {
-            Slipped.Add(args.Slipped);
-        }
-    }
+    public sealed class SlipTestSystem : TestListenerSystem<SlipEvent>;
 
     [Test]
     public async Task BananaSlipTest()
     {
-        var sys = SEntMan.System<SlipTestSystem>();
         await SpawnTarget("TrashBananaPeel");
 
         var modifier = Comp<MovementSpeedModifierComponent>(Player).SprintSpeedModifier;
         Assert.That(modifier, Is.EqualTo(1), "Player is not moving at full speed.");
 
-        // Player is to the left of the banana peel and has not slipped.
+        // Player is to the left of the banana peel.
         Assert.That(Delta(), Is.GreaterThan(0.5f));
-        Assert.That(sys.Slipped, Does.Not.Contain(SEntMan.GetEntity(Player)));
 
         // Walking over the banana slowly does not trigger a slip.
         await SetKey(EngineKeyFunctions.Walk, BoundKeyState.Down);
-        await Move(DirectionFlag.East, 1f);
+        await AssertFiresEvent<SlipEvent>(async () => await Move(DirectionFlag.East, 1f), count: 0);
+
         Assert.That(Delta(), Is.LessThan(0.5f));
-        Assert.That(sys.Slipped, Does.Not.Contain(SEntMan.GetEntity(Player)));
         AssertComp<KnockedDownComponent>(false, Player);
 
         // Moving at normal speeds does trigger a slip.
         await SetKey(EngineKeyFunctions.Walk, BoundKeyState.Up);
-        await Move(DirectionFlag.West, 1f);
-        Assert.That(sys.Slipped, Does.Contain(SEntMan.GetEntity(Player)));
+        await AssertFiresEvent<SlipEvent>(async () => await Move(DirectionFlag.West, 1f));
+
+        // And the person that slipped was the player
+        AssertEvent<SlipEvent>(predicate: @event => @event.Slipped == SPlayer);
         AssertComp<KnockedDownComponent>(true, Player);
     }
 }