add test

packages/usepreviousvalue/__tests__/usepreviousvalue.test.ts

@@ -1,7 +1,23 @@
+import { renderHook } from '@testing-library/react-hooks';
 import { usePreviousValue } from '../src';
 
+const usePreviousValueHook = () =>
+  renderHook(({ state }) => usePreviousValue(state), {
+    initialProps: { state: 0 }
+  });
+
 describe('@artifak/usepreviousvalue', () => {
-  it('needs tests', () => {
-    //
+  it('should be undefined initially', () => {
+    const { result } = usePreviousValueHook();
+    expect(result.current).toBeUndefined();
+  });
+
+  it('should return previous state value on rerender', async () => {
+    const { result, rerender } = usePreviousValueHook();
+    rerender({ state: 1 });
+    expect(result.current).toBe(0);
+
+    rerender({ state: 2 });
+    expect(result.current).toBe(1);
   });
 });