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。

普通匹配器

• toBe - toBe 使用 Object.is 来测试是否完全相等
• .not - 用来测试相反的用例
• .toEqual - 如果你想检查某个对象的值，请改用 toEqual。

toBe

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); 
});

toEqual

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}); 
});

.not

用来测试相反的用例

test('null', () => {
  const n = null;
  expect(n).not.toBeUndefined();
  expect(n).not.toBeTruthy();
});

布尔值匹配器

• toBeNull 只匹配 null
• toBeUndefined 只匹配 undefined
• toBeDefined 与 toBeUndefined 相反
• toBeTruthy 匹配任何 if 语句为真
• toBeFalsy 匹配任何 if 语句为假

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();
});

数字匹配器

• .toBeGreaterThan() - 大于
• .toBeGreaterThanOrEqual() 大于等于
• .toBeLessThan() - 小于
• .toBeLessThanOrEqual() - 小于等于
• .toBeCloseTo() - 浮点数比较

toBeGreaterThan、toBeGreaterThanOrEqual、toBeLessThan、toBeLessThanOrEqual

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); 
});

.toBeCloseTo()

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
});

字符串匹配器

• toMatch - 正则表达式的字符
• .toHaveLength(number) - 判断一个有长度的对象的长度

toMatch

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/);
});

.toHaveLength(number)

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);

数组匹配器

• .toContain(item) - 判断数组是否包含特定子项
• .toContainEqual(item) - 判断数组中是否包含一个特定对象

.toContain

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');
});

.toContainEqual(item)

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);
});

对象匹配器

• .toMatchObject(object) - 判断一个对象嵌套的 key 下面的 value 类型
• .toHaveProperty(keyPath, value) - 判断在指定的 path 下是否有这个属性

.toMatchObject(object)

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);
});

.toHaveProperty(keyPath, value)

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 tested
const 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']);
});

自定义匹配器

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:

• this.isNot
• this.equals(a, b)
• this.utils(matcherHint, printExpected and printReceived)

其他

• toThrow - 要测试的特定函数会在调用时抛出一个错误
• .resolves 和 .rejects - 用来测试 promise
• .toHaveBeenCalled() - 用来判断一个函数是否被调用过
• .toHaveBeenCalledTimes(number) - 判断函数被调用过几次

toThrow

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/);
});

.resolves 和 .rejects

用来测试 promise

//resolves
test('resolves to lemon', () => {
  // make sure to add a return statement
  return expect(Promise.resolve('lemon')).resolves.toBe('lemon');
});

//rejects
test('resolves to lemon', async () => {
  await expect(Promise.resolve('lemon')).resolves.toBe('lemon');
  await expect(Promise.resolve('lemon')).resolves.not.toBe('octopus');
});

.toHaveBeenCalled()

.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();
  });
});

.toHaveBeenCalledTimes(number)

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);
});

未整理部分

lastCalledWith

toBeCalledWith

toHaveBeenCalledWith

toHaveBeenLastCalledWith

toBeInstanceOf

toMatchSnapshot

toThrowError

toThrowErrorMatchingSnapshot