diff --git a/tests/ReactorMaintenance.Simulation.Tests/SimulationEngineTests.cs b/tests/ReactorMaintenance.Simulation.Tests/SimulationEngineTests.cs
index f1d5c8e..0efeedd 100644
--- a/tests/ReactorMaintenance.Simulation.Tests/SimulationEngineTests.cs
+++ b/tests/ReactorMaintenance.Simulation.Tests/SimulationEngineTests.cs
@@ -51,6 +51,31 @@ public sealed class SimulationEngineTests
         Assert.True(next.GetCell(new(2, 3)).Hazards.Smoke > 0);
     }
 
+    [Fact]
+    public void AdvanceTurnRunsConfiguredCellEffects()
+    {
+        var engine = new SimulationEngine([new TestCellEffect()], [], []);
+        var level = LevelState.Create("Custom effect", 6, 6)
+                              .SetCell(new(2, 2), new() {
+                                  Hazards = new() { Heat = 1 }
+                              });
+
+        var next = engine.AdvanceTurn(level);
+
+        Assert.Equal(5, next.GetCell(new(2, 2)).Hazards.Heat);
+    }
+
+    [Fact]
+    public void AdvanceTurnRunsConfiguredAreaEffects()
+    {
+        var engine = new SimulationEngine([], [new TestAreaEffect()], []);
+        var level = LevelState.Create("Custom area effect", 6, 6);
+
+        var next = engine.AdvanceTurn(level);
+
+        Assert.Equal(7, next.GetCell(new(2, 2)).Hazards.Smoke);
+    }
+
     [Fact]
     public void OverpressurePredictsPipeBurst()
     {
@@ -174,4 +199,24 @@ public sealed class SimulationEngineTests
             yield return new(EFailureKind.PipeBurst, new(turns, 0), turns, $"STEP {turns}");
         }
     }
+
+    private sealed class TestCellEffect : ISimulationEffect
+    {
+        public CellState Apply(CellState cell)
+        {
+            return cell with { Hazards = cell.Hazards with { Heat = 5 } };
+        }
+    }
+
+    private sealed class TestAreaEffect : IAreaSimulationEffect
+    {
+        public CellState[] Apply(LevelState level, CellState[] cells)
+        {
+            var next = cells.ToArray();
+            var position = new GridPosition(2, 2);
+            var cell = next[level.Index(position)];
+            next[level.Index(position)] = cell with { Hazards = cell.Hazards with { Smoke = 7 } };
+            return next;
+        }
+    }
 }
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