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Jest 实在是很方便，上手简单，几乎零配置。记录一下学习 Jest matchers。附上大部分说明及示例。
最简单的测试值的方法是看是否精确匹配。
test('two plus two is four', () => { expect(2 + 2).toBe(4); }); 如果你想检查某个对象的值，请改用 toEqual。
test('object assignment', () => { const data = {one: 1}; data['two'] = 2; expect(data).toEqual({one: 1, two: 2}); }); 用来测试相反的用例
test('null', () => { const n = null; expect(n).not.toBeUndefined(); expect(n).not.toBeTruthy();}); test('null', () => { const n = null; expect(n).toBeNull(); expect(n).toBeDefined(); expect(n).not.toBeUndefined(); expect(n).not.toBeTruthy(); expect(n).toBeFalsy();});test('zero', () => { const z = 0; expect(z).not.toBeNull(); expect(z).toBeDefined(); expect(z).not.toBeUndefined(); expect(z).not.toBeTruthy(); expect(z).toBeFalsy();}); test('two plus two', () => { const value = 2 + 2; expect(value).toBeGreaterThan(3); expect(value).toBeGreaterThanOrEqual(3.5); expect(value).toBeLessThan(5); expect(value).toBeLessThanOrEqual(4.5);// toBe 和 toEqual 对于数字来说是一样的 expect(value).toBe(4); expect(value).toEqual(4); }); 对于比较浮点数的相等，应该使用 toBeCloseTo
test('两个浮点数字相加', () => { const value = 0.1 + 0.2; // 0.30000000000000004 expect(value).toBe(0.3); // 这句会报错，因为 js 浮点数有舍入误差 expect(value).toBeCloseTo(0.3); // 这句可以运行}); 正则表达式的字符
test('there is no I in team', () => { expect('team').not.toMatch(/I/);});test('but there is a "stop" in Christoph', () => { expect('Christoph').toMatch(/stop/);}); 判断一个有长度的对象的长度
expect([1, 2, 3]).toHaveLength(3);expect('abc').toHaveLength(3);expect('').not.toHaveLength(5); 判断数组是否包含特定子项
const shoppingList = [ 'diapers', 'kleenex', 'trash bags', 'paper towels', 'beer',];test('购物清单（shopping list）里面有啤酒（beer）', () => { expect(shoppingList).toContain('beer');}); 可以判断数组中是否包含一个特定对象，类似 toEqual 与 toContain 的结合
function myBeverages() { return [ {delicious: true, sour: false}, {delicious: false, sour: true} ]}test('is delicious and not sour', () => { const myBeverage = {delicious: true, sour: false}; expect(myBeverages()).toContainEqual(myBeverage);}); 判断一个对象嵌套的 key 下面的 value 类型，需要传入一个对象。
const houseForSale = { bath: true, bedrooms: 4, kitchen: { amenities: ['oven', 'stove', 'washer'], area: 20, wallColor: 'white', },};const desiredHouse = { bath: true, kitchen: { amenities: ['oven', 'stove', 'washer'], wallColor: expect.stringMatching(/white|yellow/), },};test('the house has my desired features', () => { expect(houseForSale).toMatchObject(desiredHouse);}); 判断在指定的 path 下是否有这个属性，嵌套的 path 可以用 '.'分割，也可以用数组。
// Object containing house features to be testedconst houseForSale = { bath: true, bedrooms: 4, kitchen: { amenities: ['oven', 'stove', 'washer'], area: 20, wallColor: 'white', },};test('this house has my desired features', () => { // Simple Referencing expect(houseForSale).toHaveProperty('bath'); expect(houseForSale).toHaveProperty('bedrooms', 4); expect(houseForSale).not.toHaveProperty('pool'); // Deep referencing using dot notation expect(houseForSale).toHaveProperty('kitchen.area', 20); expect(houseForSale).toHaveProperty('kitchen.amenities', [ 'oven', 'stove', 'washer', ]); expect(houseForSale).not.toHaveProperty('kitchen.open'); // Deep referencing using an array containing the keyPath expect(houseForSale).toHaveProperty(['kitchen', 'area'], 20); expect(houseForSale).toHaveProperty( ['kitchen', 'amenities'], ['oven', 'stove', 'washer'], ); expect(houseForSale).toHaveProperty(['kitchen', 'amenities', 0], 'oven'); expect(houseForSale).not.toHaveProperty(['kitchen', 'open']);}); 使用expect.extend将自己的匹配器添加到Jest。自定义匹配器需要返回一个包含两个key 的对象
{ pass：false //‘布尔值’， message： () => 'message string' //‘函数，该函数返回一个提示信息’} expect.extend({ toBeDivisibleBy(received, argument) { const pass = received % argument == 0; if (pass) { return { message: () => `expected ${received} not to be divisible by ${argument}`, pass: true, }; } else { return { message: () => `expected ${received} to be divisible by ${argument}`, pass: false, }; } },});test('even and odd numbers', () => { expect(100).toBeDivisibleBy(2); expect(101).not.toBeDivisibleBy(2);}); 这些帮助函数可以在自定义匹配器中的this中找到:
要测试的特定函数会在调用时抛出一个错误
function compileAndroidCode() { throw new ConfigError('you are using the wrong JDK');}test('compiling android goes as expected', () => { expect(compileAndroidCode).toThrow(); expect(compileAndroidCode).toThrow(ConfigError); // You can also use the exact error message or a regexp expect(compileAndroidCode).toThrow('you are using the wrong JDK'); expect(compileAndroidCode).toThrow(/JDK/);}); 用来测试 promise
//resolvestest('resolves to lemon', () => { // make sure to add a return statement return expect(Promise.resolve('lemon')).resolves.toBe('lemon');});//rejectstest('resolves to lemon', async () => { await expect(Promise.resolve('lemon')).resolves.toBe('lemon'); await expect(Promise.resolve('lemon')).resolves.not.toBe('octopus');}); .toHaveBeenCalled() 也有个别名是.toBeCalled()，用来判断一个函数是否被调用过。
describe('drinkAll', () => { test('drinks something lemon-flavored', () => { const drink = jest.fn(); drinkAll(drink, 'lemon'); expect(drink).toHaveBeenCalled(); }); test('does not drink something octopus-flavored', () => { const drink = jest.fn(); drinkAll(drink, 'octopus'); expect(drink).not.toHaveBeenCalled(); });}); 和 toHaveBeenCalled 类似，判断函数被调用过几次。
test('drinkEach drinks each drink', () => { const drink = jest.fn(); drinkEach(drink, ['lemon', 'octopus']); expect(drink).toHaveBeenCalledTimes(2);});
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作者：woodccc 链接：https://www.jianshu.com/p/c1b5676c1edd 来源：简书 著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。