jest 学习：匹配器的使用

参考官方文档的这一段：Jest使用“匹配器”的机制让你可以使用各种方法进行测试

toBe: 精确匹配

test('2 加 2 等于 4', () => {
  expect(2 + 2).toBe(4);
});

toEqual: 对象比较

test('对象赋值', () => {
  const data = {one: 1};
  data['two'] = 2;
  expect(data).toEqual({one: 1, two: 2});
});

not: 相反的比较

test('adding positive numbers is not zero', () => {
  for (let a = 1; a < 10; a++) {
    for (let b = 1; b < 10; b++) {
      expect(a + b).not.toBe(0);
    }
  }
});

JS 的常用真/假值

• 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();
});

目前没有明白场景的比较(toBe/toEqual感觉可以代替)

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 and toEqual are equivalent for numbers
  expect(value).toBe(4);
  expect(value).toEqual(4);
});

toBeCloseTo对于0.1+0.2 此类情况的比较

> 0.1 + 0.2
0.30000000000000004

test("两个浮点数字相加", () => {
  const value = 0.1 + 0.2;
  //expect(value).toBe(0.3);           这句会报错，因为浮点数有舍入误差
  expect(value).toBeCloseTo(0.3); // 这句可以运行
});

toMatch: 可以检查对具有 toMatch 正则表达式的字符串

test("there is no I in team", () => {
  expect("team").not.toMatch(/I/);
});

test('but there is a "stop" in Christoph', () => {
  expect("Christoph").toMatch(/stop/);
});

toContain：检查一个数组或可迭代对象是否包含某个特定项

const shoppingList = [
  'diapers',
  'kleenex',
  'trash bags',
  'paper towels',
  'milk',
];

test('the shopping list has milk on it', () => {
  expect(shoppingList).toContain('milk');
  expect(new Set(shoppingList)).toContain('milk');
});

toThrow：有关异常的比较

function compileAndroidCode() {
  throw new Error('you are using the wrong JDK');
}

test('compiling android goes as expected', () => {
  expect(() => compileAndroidCode()).toThrow();
  expect(() => compileAndroidCode()).toThrow(Error);

  // You can also use the exact error message or a regexp
  expect(() => compileAndroidCode()).toThrow('you are using the wrong JDK');
  expect(() => compileAndroidCode()).toThrow(/JDK/);
});

参考

https://jestjs.io/zh-Hans/docs/using-matchers