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diff --git a/src/eventx.test.ts b/src/eventx.test.ts
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+++ b/src/eventx.test.ts
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+import { describe, test, expect, vi, beforeEach } from "vitest";
+import EventX from "./eventx";
+
+describe("EventX", () => {
+  describe("subscribe", () => {
+    test("subscribes to an event", () => {
+      const $ = EventX({ counter: 1 });
+      const id = $.subscribe("test-event", (state) => ({ state }));
+      expect(id).toBe(1);
+      expect($.subscriptionCount("test-event")).toBe(1);
+    });
+
+    test("subscribes to an event once", () => {
+      const $ = EventX({ counter: 1 });
+      const id = $.subscribeOnce("test-event", (state) => ({ state }));
+      expect(id).toBe(1);
+      expect($.subscriptionCount("test-event")).toBe(1);
+
+      // Dispatch the event to trigger the one-time subscription
+      $.dispatch("test-event");
+      expect($.subscriptionCount("test-event")).toBe(0);
+    });
+
+    test("unsubscribes from an event", () => {
+      const $ = EventX({ counter: 1 });
+      $.subscribe("test-event", (state) => ({ state }));
+      expect($.subscriptionCount("test-event")).toBe(1);
+
+      $.unsubscribe("test-event");
+      expect($.subscriptionCount("test-event")).toBe(0);
+    });
+  });
+
+  describe("dispatch", () => {
+    test("dispatches an event without arguments", () => {
+      const $ = EventX({ counter: 1 });
+      const callback = vi.fn((state) => ({ state }));
+
+      $.subscribe("test-event", callback);
+      $.dispatch("test-event");
+
+      expect(callback).toHaveBeenCalledTimes(1);
+      expect(callback).toHaveBeenCalledWith({ counter: 1 });
+    });
+
+    test("dispatches an event with arguments", () => {
+      const $ = EventX({ counter: 1 });
+      const callback = vi.fn((state, arg1, arg2) => ({ state }));
+
+      $.subscribe("test-event", callback);
+      $.dispatch("test-event", "arg1-value", "arg2-value");
+
+      expect(callback).toHaveBeenCalledTimes(1);
+      expect(callback).toHaveBeenCalledWith({ counter: 1 }, "arg1-value", "arg2-value");
+    });
+
+    test("updates state when event handler returns new state", () => {
+      const $ = EventX({ counter: 1 });
+      const stateChangeSpy = vi.fn((state) => ({ state }));
+
+      $.subscribe("$counter", stateChangeSpy);
+      $.subscribe("increment", (state) => ({
+        state: { ...state, counter: state.counter + 1 },
+      }));
+
+      $.dispatch("increment");
+
+      expect(stateChangeSpy).toHaveBeenCalledTimes(1);
+      expect(stateChangeSpy).toHaveBeenCalledWith({ counter: 2 });
+    });
+
+    test("dispatches nested events", () => {
+      const $ = EventX({ counter: 1 });
+      const nestedEventSpy = vi.fn((state) => ({ state }));
+
+      $.subscribe("nested-event", nestedEventSpy);
+      $.subscribe("parent-event", (state) => ({
+        state,
+        dispatch: { eventName: "nested-event" },
+      }));
+
+      $.dispatch("parent-event");
+
+      expect(nestedEventSpy).toHaveBeenCalledTimes(1);
+    });
+
+    test("dispatches multiple nested events", () => {
+      const $ = EventX({ counter: 1 });
+      const nestedEvent1Spy = vi.fn((state) => ({ state }));
+      const nestedEvent2Spy = vi.fn((state) => ({ state }));
+
+      $.subscribe("nested-event-1", nestedEvent1Spy);
+      $.subscribe("nested-event-2", nestedEvent2Spy);
+      $.subscribe("parent-event", (state) => ({
+        state,
+        dispatch: [{ eventName: "nested-event-1" }, { eventName: "nested-event-2" }],
+      }));
+
+      $.dispatch("parent-event");
+
+      expect(nestedEvent1Spy).toHaveBeenCalledTimes(1);
+      expect(nestedEvent2Spy).toHaveBeenCalledTimes(1);
+    });
+
+    test("dispatches nested events with arguments", () => {
+      const $ = EventX({ counter: 1 });
+      const nestedEventSpy = vi.fn((state, arg) => ({ state }));
+
+      $.subscribe("nested-event", nestedEventSpy);
+      $.subscribe("parent-event", (state) => ({
+        state,
+        dispatch: { eventName: "nested-event", args: ["arg-value"] },
+      }));
+
+      $.dispatch("parent-event");
+
+      expect(nestedEventSpy).toHaveBeenCalledTimes(1);
+      expect(nestedEventSpy).toHaveBeenCalledWith({ counter: 1 }, "arg-value");
+    });
+  });
+
+  describe("state change detection", () => {
+    test("detects value changes in state", () => {
+      const $ = EventX({ counter: 1, nested: { value: "test" } });
+      const counterChangeSpy = vi.fn((state) => ({ state }));
+
+      $.subscribe("$counter", counterChangeSpy);
+      $.subscribe("change-counter", (state) => ({
+        state: { ...state, counter: 2 },
+      }));
+
+      $.dispatch("change-counter");
+
+      expect(counterChangeSpy).toHaveBeenCalledTimes(1);
+      expect(counterChangeSpy).toHaveBeenCalledWith({ counter: 2, nested: { value: "test" } });
+    });
+
+    test("detects nested value changes in state", () => {
+      const $ = EventX({ counter: 1, nested: { value: "test" } });
+      const nestedValueChangeSpy = vi.fn((state) => ({ state }));
+
+      $.subscribe("$nested.value", nestedValueChangeSpy);
+      $.subscribe("change-nested-value", (state) => ({
+        state: {
+          ...state,
+          nested: { ...state.nested, value: "changed" },
+        },
+      }));
+
+      $.dispatch("change-nested-value");
+
+      expect(nestedValueChangeSpy).toHaveBeenCalledTimes(1);
+      expect(nestedValueChangeSpy).toHaveBeenCalledWith({
+        counter: 1,
+        nested: { value: "changed" },
+      });
+    });
+
+    test("detects deleted properties in state", () => {
+      const $ = EventX({ counter: 1, toDelete: "value" } as { counter: number; toDelete?: string });
+      const deleteChangeSpy = vi.fn((state) => ({ state }));
+
+      $.subscribe("$toDelete", deleteChangeSpy);
+      $.subscribe("delete-property", (state) => {
+        const newState = { counter: state.counter };
+        return { state: newState };
+      });
+
+      $.dispatch("delete-property");
+
+      expect(deleteChangeSpy).toHaveBeenCalledTimes(1);
+    });
+
+    test("detects type changes in state", () => {
+      const $ = EventX({ counter: 1 } as { counter: string | number });
+      const counterChangeSpy = vi.fn((state) => ({ state }));
+
+      $.subscribe("$counter", counterChangeSpy);
+      $.subscribe("change-counter-type", (state) => ({
+        state: { ...state, counter: "string now" },
+      }));
+
+      $.dispatch("change-counter-type");
+
+      expect(counterChangeSpy).toHaveBeenCalledTimes(1);
+    });
+  });
+
+  describe("utility methods", () => {
+    test("returns all subscription names", () => {
+      const $ = EventX({ counter: 1 });
+      $.subscribe("event1", (state) => ({ state }));
+      $.subscribe("event2", (state) => ({ state }));
+
+      const subs = $.subscriptions();
+      expect(subs).toContain("event1");
+      expect(subs).toContain("event2");
+      expect(subs.length).toBe(2);
+    });
+
+    test("returns subscription count for specific event", () => {
+      const $ = EventX({ counter: 1 });
+      $.subscribe("event1", (state) => ({ state }));
+      $.subscribe("event1", (state) => ({ state }));
+      $.subscribe("event2", (state) => ({ state }));
+
+      expect($.subscriptionCount("event1")).toBe(2);
+      expect($.subscriptionCount("event2")).toBe(1);
+    });
+  });
+});