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reactUtils.test.ts
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/
reactUtils.test.ts
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/**
* Copyright (c) Facebook, Inc. and its affiliates.
*
* This source code is licensed under the MIT license found in the
* LICENSE file in the root directory of this source tree.
*/
import {renderHook} from '@testing-library/react-hooks';
import {usePrevious, useShallowMemoObject} from '../reactUtils';
describe('usePrevious', () => {
it('returns the previous value of a variable', () => {
const {result, rerender} = renderHook((val) => usePrevious(val), {
initialProps: 1,
});
expect(result.current).toBeUndefined();
rerender(2);
expect(result.current).toBe(1);
rerender(3);
expect(result.current).toBe(2);
});
});
describe('useShallowMemoObject', () => {
it('can memoize object', () => {
const someObj = {hello: 'world'};
const someArray = ['hello', 'world'];
const obj1 = {a: 1, b: '2', someObj, someArray};
const {result, rerender} = renderHook((val) => useShallowMemoObject(val), {
initialProps: obj1,
});
expect(result.current).toBe(obj1);
const obj2 = {a: 1, b: '2', someObj, someArray};
rerender(obj2);
expect(result.current).toBe(obj1);
const obj3 = {a: 1, b: '2', someObj, someArray};
rerender(obj3);
expect(result.current).toBe(obj1);
// Current implementation is basic and sensitive to order
const obj4 = {b: '2', a: 1, someObj, someArray};
rerender(obj4);
expect(result.current).toBe(obj4);
const obj5 = {b: '2', a: 1, someObj, someArray};
rerender(obj5);
expect(result.current).toBe(obj4);
const obj6 = {b: '2', a: 1, someObj: {...someObj}, someArray};
rerender(obj6);
expect(result.current).toBe(obj6);
});
});