[Test Improver] Add unit tests for useInterval composable

shell/composables/useInterval.test.ts

@@ -0,0 +1,106 @@
+import { defineComponent } from 'vue';
+import { mount } from '@vue/test-utils';
+import { useInterval } from './useInterval';
+
+function createHarness(fn: () => void, delay: number) {
+  return defineComponent({
+    setup() {
+      useInterval(fn, delay);
+    },
+    template: '<div />',
+  });
+}
+
+describe('useInterval', () => {
+  beforeEach(() => {
+    jest.useFakeTimers();
+  });
+
+  afterEach(() => {
+    jest.useRealTimers();
+  });
+
+  it('does not call fn before the component is mounted', () => {
+    const fn = jest.fn();
+
+    createHarness(fn, 1000);
+
+    expect(fn).not.toHaveBeenCalled();
+  });
+
+  it('calls fn after the specified delay once mounted', () => {
+    const fn = jest.fn();
+
+    mount(createHarness(fn, 1000));
+
+    expect(fn).not.toHaveBeenCalled();
+    jest.advanceTimersByTime(1000);
+    expect(fn).toHaveBeenCalledTimes(1);
+  });
+
+  it('calls fn repeatedly on each interval tick', () => {
+    const fn = jest.fn();
+
+    mount(createHarness(fn, 500));
+
+    jest.advanceTimersByTime(1500);
+    expect(fn).toHaveBeenCalledTimes(3);
+  });
+
+  it('does not call fn before the delay elapses', () => {
+    const fn = jest.fn();
+
+    mount(createHarness(fn, 200));
+
+    jest.advanceTimersByTime(199);
+    expect(fn).not.toHaveBeenCalled();
+
+    jest.advanceTimersByTime(1);
+    expect(fn).toHaveBeenCalledTimes(1);
+  });
+
+  it('clears the interval on unmount so fn is not called afterwards', () => {
+    const fn = jest.fn();
+    const wrapper = mount(createHarness(fn, 1000));
+
+    jest.advanceTimersByTime(1000);
+    expect(fn).toHaveBeenCalledTimes(1);
+
+    wrapper.unmount();
+    jest.advanceTimersByTime(2000);
+    expect(fn).toHaveBeenCalledTimes(1);
+  });
+
+  it('stops calling fn immediately when unmounted mid-interval', () => {
+    const fn = jest.fn();
+    const wrapper = mount(createHarness(fn, 1000));
+
+    jest.advanceTimersByTime(500);
+    wrapper.unmount();
+
+    jest.advanceTimersByTime(1000);
+    expect(fn).not.toHaveBeenCalled();
+  });
+
+  it.each([
+    {
+      desc:  'short delay (100 ms) fires correct count',
+      delay: 100,
+      time:  350,
+      calls: 3,
+    },
+    {
+      desc:  'long delay (2000 ms) fires correct count',
+      delay: 2000,
+      time:  5000,
+      calls: 2,
+    },
+  ])('$desc', ({ delay, time, calls }) => {
+    const fn = jest.fn();
+
+    mount(createHarness(fn, delay));
+    jest.advanceTimersByTime(time);
+
+    expect(fn).toHaveBeenCalledTimes(calls);
+  });
+});