prometheus

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import { useLocalStorage } from './useLocalStorage';
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import { renderHook, act } from '@testing-library/react-hooks';
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describe('useLocalStorage', () => {
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  it('returns the initialState', () => {
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    const initialState = { a: 1, b: 2 };
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    const { result } = renderHook(() => useLocalStorage('mystorage', initialState));
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    expect(result.current[0]).toEqual(initialState);
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  });
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  it('stores the initialState as serialized json in localstorage', () => {
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    const key = 'mystorage';
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    const initialState = { a: 1, b: 2 };
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    renderHook(() => useLocalStorage(key, initialState));
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    expect(localStorage.getItem(key)).toEqual(JSON.stringify(initialState));
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  });
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  it('returns a setValue function that can reset local storage', () => {
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    const key = 'mystorage';
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    const initialState = { a: 1, b: 2 };
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    const { result } = renderHook(() => useLocalStorage(key, initialState));
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    const newValue = { a: 2, b: 5 };
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    act(() => {
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      result.current[1](newValue);
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    });
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    expect(result.current[0]).toEqual(newValue);
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    expect(localStorage.getItem(key)).toEqual(JSON.stringify(newValue));
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  });
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  it('localStorage.getItem calls once', () => {
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    // do not prepare the initial state on every render except the first
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    const spyStorage = jest.spyOn(Storage.prototype, 'getItem') as jest.Mock;
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    const key = 'mystorage';
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    const initialState = { a: 1, b: 2 };
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    const { result } = renderHook(() => useLocalStorage(key, initialState));
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    const newValue = { a: 2, b: 5 };
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    act(() => {
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      result.current[1](newValue);
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    });
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    expect(spyStorage).toHaveBeenCalledTimes(1);
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    spyStorage.mockReset();
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  });
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});
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