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import { renderHook } from '@testing-library/react-hooks';
import { useInterval } from '../src';
let callback;
beforeEach(() => {
callback = jest.fn();
});
beforeAll(() => {
jest.useFakeTimers();
});
afterEach(() => {
callback.mockRestore();
jest.clearAllTimers();
});
afterAll(() => {
jest.useRealTimers();
});
it('should init hook with default delay', () => {
const { result } = renderHook(() => useInterval(callback));
expect(result.current).toBeUndefined();
expect(setInterval).toHaveBeenCalledTimes(1);
// if not delay provided, it's assumed as 0
expect(setInterval).toHaveBeenCalledWith(expect.any(Function), 0);
});
it('should init hook with custom delay', () => {
const { result } = renderHook(() => useInterval(callback, 5000));
expect(result.current).toBeUndefined();
expect(setInterval).toHaveBeenCalledTimes(1);
expect(setInterval).toHaveBeenCalledWith(expect.any(Function), 5000);
});
it('should init hook without delay', () => {
const { result } = renderHook(() => useInterval(callback, null));
expect(result.current).toBeUndefined();
// if null delay provided, it's assumed as no delay
expect(setInterval).not.toHaveBeenCalled();
});
it('should repeatedly calls provided callback with a fixed time delay between each call', () => {
renderHook(() => useInterval(callback, 200));
expect(callback).not.toHaveBeenCalled();
// fast-forward time until 1s before it should be executed
jest.advanceTimersByTime(199);
expect(callback).not.toHaveBeenCalled();
// fast-forward until 1st call should be executed
jest.advanceTimersByTime(1);
expect(callback).toHaveBeenCalledTimes(1);
// fast-forward until next timer should be executed
jest.advanceTimersToNextTimer();
expect(callback).toHaveBeenCalledTimes(2);
// fast-forward until 3 more timers should be executed
jest.advanceTimersToNextTimer(3);
expect(callback).toHaveBeenCalledTimes(5);
});
it('should clear interval on unmount', () => {
const { unmount } = renderHook(() => useInterval(callback, 200));
const initialTimerCount = jest.getTimerCount();
expect(clearInterval).not.toHaveBeenCalled();
unmount();
expect(clearInterval).toHaveBeenCalledTimes(1);
expect(jest.getTimerCount()).toBe(initialTimerCount - 1);
});
it('should handle new interval when delay is updated', () => {
let delay = 200;
const { rerender } = renderHook(() => useInterval(callback, delay));
expect(callback).not.toHaveBeenCalled();
// fast-forward initial delay
jest.advanceTimersByTime(200);
expect(callback).toHaveBeenCalledTimes(1);
// update delay by increasing previous one
delay = 500;
rerender();
// fast-forward initial delay again but this time it should not execute the cb
jest.advanceTimersByTime(200);
expect(callback).toHaveBeenCalledTimes(1);
// fast-forward remaining time for new delay
jest.advanceTimersByTime(300);
expect(callback).toHaveBeenCalledTimes(2);
});
it('should clear pending interval when delay is updated', () => {
let delay = 200;
const { rerender } = renderHook(() => useInterval(callback, delay));
expect(clearInterval).not.toHaveBeenCalled();
const initialTimerCount = jest.getTimerCount();
// update delay while there is a pending interval
delay = 500;
rerender();
expect(clearInterval).toHaveBeenCalledTimes(1);
expect(jest.getTimerCount()).toBe(initialTimerCount);
});
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