IgnusG / test-preact-hooks

Testing for preact hooks

test-preact-hooks ⚓️

Simple testing for preact hooks

This is a fork of the awesome test-react-hooks library migrated to preact - check it out

Example usage can be found at this sandbox

Contents

• test-preact-hooks ⚓️
  • Contents
  • Get Started
  • Api
    • useTestProxy
      • Arguments
      • Result
    • cleanup
    • act

Get Started

To install either :

yarn add test-preact-hooks -D or npm i test-preact-hooks --save-dev

test-preact-hooks needs a dom to work, if you're running jest you should be good to go. For anything else consult your testing framework of choice.

Example

import { createTestProxy, cleanUp } from "test-preact-hooks";
import { useState } from "preact/hooks";

// Cleans up the dom container that's created during testing
// For jest users just add to setupFilesAfterEnv
afterEach(() => cleanUp());

// Create your hook
const useCounter = (initial = 0, inc = 1) => {
  const [count, setCount] = useState(initial);
  const inc = () => setCount(count + inc);
  return {
    count,
    inc,
  };
};

// Proxy of your hook, use it like you would in a component
// Internally calls render for the hook and act on everything else
const [prxCounter] = createTestProxy(useCounter);

it("will increment by one", () => {
  {
    const { count, inc } = prxCounter();
    expect(count).toBe(0);
    inc();
  }

  {
    const { count } = prxCounter();
    expect(count).toBe(1);
  }
});

it("start with a new initial amount", () => {
  {
    const { count, inc } = prxCounter(4);
    expect(count).toBe(4);
    inc();
  }

  {
    const { count } = prxCounter(4);
    expect(count).toBe(5);
  }
});

it("will increment by a new amount", () => {
  {
    const { count, inc } = prxCounter(0, 2);
    expect(count).toBe(0);
    inc();
  }

  {
    const { count } = prxCounter(0, 2);
    expect(count).toBe(2);
  }
});

Api

createTestProxy

createTestProxy<THook, TProps = any>(hook: THook,options: UseProxyOptions<TProps> = {}) => [THook, HookControl<TProps>]

Creates a proxy of the hook passed in for testing.

Arguments

• hook : hook to be tested

• options : optional options to render the hook with

  /**
   * Options for createTestProxy
   *
   * @export
   * @interface UseProxyOptions
   * @template TProps
   */
  export interface UseProxyOptions<TProps> {
    /**
     * Component to wrap the test component in
     *
     * @type {ComponentType<TProps>}
     */
    wrapper?: ComponentType<TProps>;
  
    /**
     * Initial  props to render the wrapper component with
     */
    props?: TProps;
  
    /**
     * Toggle if result of hook should be wrapped in a proxy - set to true to check for strict equality
     */
    shallow?: boolean;
  }

Result

Tuple with the first element being a proxy hook and it's control object

[THook, HookControl<TProps>]

• THook - A proxy of the hook argument, each call to the hook will call render

• HookControl<TProps> - Control object for the proxy hook

  /**
   * Control object for the proxy hook
   *
   * @export
   * @interface HookControl
   * @template TProps
   */
  export interface HookControl<TProps> {
    /**
     * Unmounts the test component
     * useful when testing the cleanup of useEffect or useLayoutEffect
     *
     * @memberof HookControl
     */
    unmount: () => void;
    /**
     * Updates the props to be used in the wrapper component
     * Does not cause a rerender, call the proxy hook to force that
     */
    props: TProps;
    /**
     * The container of the test component
     */
    readonly container: HTMLElement;
    /**
     * A promise that will resolve on update
     * Use when waiting for async effects to run
     */
    waitForNextUpdate: () => Promise<void>;
  }

If you chose to use shallow: true the result of the proxy will not be wrapped in a proxy. This can cause instability with complex hooks but can be used to check for strict equality (for example if a hook should return an exact object copy for useMemo or useEffect comparison).

cleanup

cleanUp():void

Function to be called after your tests to clean up the container created during tests and unmount the hook.

act

act(callback: () => void):void

Re-exported from preact/test-utils

Use this if your updating the dom outside the hook.

For an example on correct usage check out dom event example