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usePrevious.test.ts
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usePrevious.test.ts
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import React from 'react'
import {usePrevious} from './usePrevious'
import {renderHook, act, cleanup} from '@testing-library/react-hooks'
describe('usePrevious', () => {
afterEach(cleanup)
it('returns previous value', () => {
const {result} = renderHook(() => {
const [value, setValue] = React.useState(1)
const previous = usePrevious(value)
return {previous, setValue}
})
expect(result.current.previous).toEqual([])
act(() => {
result.current.setValue(2)
})
expect(result.current.previous).toEqual([1])
act(() => {
result.current.setValue(2)
})
expect(result.current.previous).toEqual([1])
act(() => {
result.current.setValue(3)
})
act(() => {
result.current.setValue(4)
})
expect(result.current.previous).toEqual([3])
})
it('returns multiple previous values', () => {
const {result} = renderHook(() => {
const [value, setValue] = React.useState(1)
const previous = usePrevious(value, 3)
return {previous, setValue}
})
expect(result.current.previous).toEqual([])
act(() => {
result.current.setValue(2)
})
expect(result.current.previous).toEqual([1])
act(() => {
result.current.setValue(2)
})
expect(result.current.previous).toEqual([1])
act(() => {
result.current.setValue(3)
})
act(() => {
result.current.setValue(4)
})
expect(result.current.previous).toEqual([3, 2, 1])
act(() => {
result.current.setValue(5)
})
expect(result.current.previous).toEqual([4, 3, 2])
})
})