diff --git a/src/main/java/com/livingworld/testing/TestSimulationModule.java b/src/main/java/com/livingworld/testing/TestSimulationModule.java
new file mode 100644
index 0000000..ea02bbe
--- /dev/null
+++ b/src/main/java/com/livingworld/testing/TestSimulationModule.java
@@ -0,0 +1,103 @@
+package com.livingworld.testing;
+
+import com.livingworld.data.serialization.PersistenceReader;
+import com.livingworld.data.serialization.PersistenceWriter;
+import com.livingworld.events.LivingWorldEvent;
+import com.livingworld.modules.ModuleContext;
+import com.livingworld.modules.ModuleMetadata;
+import com.livingworld.modules.ModuleUpdateResult;
+import com.livingworld.modules.RegionUpdateContext;
+import com.livingworld.modules.ServerContext;
+import com.livingworld.modules.SimulationModule;
+import com.livingworld.regions.Region;
+import java.util.List;
+
+/**
+ * Deterministic module used to exercise the simulation engine in tests.
+ */
+public final class TestSimulationModule implements SimulationModule {
+
+    public static final String MODULE_ID = "test";
+
+    private static final ModuleMetadata METADATA = new ModuleMetadata(
+            MODULE_ID,
+            "Test Simulation Module",
+            "1.0.0",
+            "Deterministic module for engine tests.",
+            "1",
+            List.of(),
+            List.of(),
+            true,
+            true,
+            false);
+
+    private boolean initialized;
+    private int updateCount;
+
+    @Override
+    public String getModuleId() {
+        return MODULE_ID;
+    }
+
+    @Override
+    public ModuleMetadata getMetadata() {
+        return METADATA;
+    }
+
+    @Override
+    public void initialize(ModuleContext context) {
+        if (context == null) {
+            throw new IllegalArgumentException("context must not be null");
+        }
+        initialized = true;
+    }
+
+    @Override
+    public void onServerStarted(ServerContext context) {
+        // No server resources are needed by the test module.
+    }
+
+    @Override
+    public void createDefaultRegionData(Region region) {
+        // The test module keeps deterministic counters outside region data.
+    }
+
+    @Override
+    public ModuleUpdateResult updateRegion(RegionUpdateContext context) {
+        if (context == null) {
+            throw new IllegalArgumentException("context must not be null");
+        }
+        updateCount++;
+        return updateCount % 10 == 0
+                ? ModuleUpdateResult.changed()
+                : ModuleUpdateResult.noChange();
+    }
+
+    @Override
+    public void onLivingWorldEvent(LivingWorldEvent event) {
+        // The test module does not consume events.
+    }
+
+    @Override
+    public void saveModuleData(PersistenceWriter writer) {
+        // The counter is intentionally transient test state.
+    }
+
+    @Override
+    public void loadModuleData(PersistenceReader reader) {
+        // The counter is intentionally transient test state.
+    }
+
+    @Override
+    public void shutdown() {
+        // No resources to release.
+    }
+
+    public boolean isInitialized() {
+        return initialized;
+    }
+
+    public int getUpdateCount() {
+        return updateCount;
+    }
+}