add test with object cycles

tests/17_cycles.spec.ts

@@ -0,0 +1,46 @@
+import { describe, expect, it } from 'vitest';
+import { createProxy, isChanged } from 'proxy-compare';
+
+const noop = (_arg: unknown) => {
+  // do nothing
+};
+
+describe('object with cycles', () => {
+  interface S {
+    a: string;
+    s?: S;
+  }
+
+  it('without cache', () => {
+    const s1: S = { a: 'a' };
+    s1.s = s1;
+    const s2: S = { a: 'a' };
+    s2.s = s2;
+    const a1 = new WeakMap();
+    const p1 = createProxy(s1, a1);
+    noop(p1.s?.a);
+    expect(() => isChanged(s1, s2, a1)).toThrow();
+  });
+
+  it('with cache', () => {
+    const s1: S = { a: 'a' };
+    s1.s = s1;
+    const s2: S = { a: 'a' };
+    s2.s = s2;
+    const a1 = new WeakMap();
+    const p1 = createProxy(s1, a1);
+    noop(p1.s?.a);
+    expect(isChanged(s1, s2, a1, new WeakMap())).toBe(false);
+  });
+
+  it('with cache with a change', () => {
+    const s1: S = { a: 'a' };
+    s1.s = s1;
+    const s2: S = { a: 'aa' };
+    s2.s = s2;
+    const a1 = new WeakMap();
+    const p1 = createProxy(s1, a1);
+    noop(p1.s?.a);
+    expect(isChanged(s1, s2, a1, new WeakMap())).toBe(true);
+  });
+});