test: tighten wait forever interval assertion

src/cli/cli-utils.test.ts

@@ -11,11 +11,20 @@ import { waitForever } from "./wait.js";
 
 describe("waitForever", () => {
   it("creates an unref'ed interval and returns a pending promise", () => {
-    const setIntervalSpy = vi.spyOn(global, "setInterval");
-    const promise = waitForever();
-    expect(setIntervalSpy).toHaveBeenCalledWith(expect.any(Function), 1_000_000);
-    expect(promise).toBeInstanceOf(Promise);
-    setIntervalSpy.mockRestore();
+    const unref = vi.fn();
+    const interval = { unref } as unknown as ReturnType<typeof setInterval>;
+    const setIntervalSpy = vi.spyOn(global, "setInterval").mockReturnValue(interval);
+    try {
+      const promise = waitForever();
+      expect(setIntervalSpy).toHaveBeenCalledTimes(1);
+      const [callback, delay] = setIntervalSpy.mock.calls[0] ?? [];
+      expect(typeof callback).toBe("function");
+      expect(delay).toBe(1_000_000);
+      expect(unref).toHaveBeenCalledTimes(1);
+      expect(promise).toBeInstanceOf(Promise);
+    } finally {
+      setIntervalSpy.mockRestore();
+    }
   });
 });