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preact-hooks-testing-library

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preact port of the the @testing-library/react-hooks library.

Why not @testing-library/react-hooks?

Currently, due to the use of react-test-renderer, the react hooks testing library most likely will never be compatible with preact.

Why not another library?

At the time of writing, a library did not exist to test preact hooks.

When to use this library

  1. You're writing a library with one or more custom hooks that are not directly tied to a component
  2. You have a complex hook that is difficult to test through component interactions

When not to use this library

  1. Your hook is defined alongside a component and is only used there
  2. Your hook is easy to test by just testing the components using it

Installation

Install with your favorite package manager

yarn add -D @testing-library/preact-hooks
OR
npm install --save-dev @testing-library/preact-hooks

Example #1: Basic


useCounter.ts

import { useState, useCallback } from 'preact/hooks';

const useCounter = () => {
    const [count, setCount] = useState(0);

    const increment = useCallback(() => setCount(c => c + 1));

    return {
        count,
        increment
    }
}

export default useCounter;

useCounter.test.ts

import { renderHook, act } from '@testing-library/preact-hooks';
import useCounter from './useCounter';

test('should increment counter', () => {
  const { result } = renderHook(() => useCounter());

  act(() => {
    result.current.increment();
  });

  expect(result.current.count).toBe(1);
});

Example #2: Wrapped Components

Sometimes, hooks may need access to values or functionality outside of itself that are provided by a context provider or some other HOC.

import { createContext } from 'preact'
import { useState, useCallback, useContext } from 'preact/hooks'

const CounterStepContext = createContext(1)
export const CounterStepProvider = ({ step, children }) => (
  <CounterStepContext.Provider value={step}>{children}</CounterStepContext.Provider>
)
export function useCounter(initialValue = 0) {
  const [count, setCount] = useState(initialValue)
  const step = useContext(CounterStepContext)
  const increment = useCallback(() => setCount((x) => x + step), [step])
  const reset = useCallback(() => setCount(initialValue), [initialValue])
  return { count, increment, reset }
}

In our test, we simply use CoounterStepProvider as the wrapper when rendering the hook:

import { renderHook, act } from '@testing-library/preact-hooks'
import { CounterStepProvider, useCounter } from './counter'

test('should use custom step when incrementing', () => {
  const wrapper = ({ children }) => <CounterStepProvider step={2}>{children}</CounterStepProvider>
  const { result } = renderHook(() => useCounter(), { wrapper })
  act(() => {
    result.current.increment()
  })
  expect(result.current.count).toBe(2)
})

TODO

  • remove @ts-nocheck flag from tests
  • fix disabled auto clean up tests

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Simple and complete Preact hooks testing utilities that encourage good testing practices.

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