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toBe

完全相等

test('two plus two is four', () => {
  expect(2 + 2).toBe(4);
});

toEqual

对象完全相等

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

Truthiness

判断是否为空，在undefined、null、false之间。

• toBeNull 只匹配Null
• toBeUndefined 只匹配undefined
• toBeDefined 是否定义
• toBeTruthy 匹配是否true
• toBeFalsy 匹配是否false

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();
});

Numbers

• toBeGreaterThan 大于
• toBeGreaterThanOrEqual 大于等于
• toBeLessThan 小于
• toBeLessThanOrEqual 小于等于
• toBeCloseTo 浮点数相等

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);
});

test('adding floating point numbers', () => {
  const value = 0.1 + 0.2;
  //expect(value).toBe(0.3);           This won't work because of rounding error
  expect(value).toBeCloseTo(0.3); // This works.
});

Strings

• toMatch 来检查字符串和正则表达式

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

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

Arrays and iterables

• toContain 包含

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');
});

Exceptions

• toThrow 异常比较

抛出异常的函数需要在包装函数中调用，否则 toThrow 断言将失败。

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/);
});

异步代码测试

Callbacks

test('the data is peanut butter', done => {
  function callback(data) {
    try {
      expect(data).toBe('peanut butter');
      done();
    } catch (error) {
      done(error);
    }
  }

  fetchData(callback);
});

Promises

test('the data is peanut butter', () => {
  return fetchData().then(data => {
    expect(data).toBe('peanut butter');
  });
});

如果你希望一个承诺被拒绝，使用。捕捉法。确保添加 expect.assertions 来验证调用了一定数量的断言。否则，一个实现的承诺就不会失败。

test('the fetch fails with an error', () => {
  expect.assertions(1);
  return fetchData().catch(e => expect(e).toMatch('error'));
});

.resolves / .rejects

test('the data is peanut butter', () => {
  return expect(fetchData()).resolves.toBe('peanut butter');
});

test('the fetch fails with an error', () => {
  return expect(fetchData()).rejects.toMatch('error');
});

Async/Await

test('the data is peanut butter', async () => {
  const data = await fetchData();
  expect(data).toBe('peanut butter');
});

test('the fetch fails with an error', async () => {
  expect.assertions(1);
  try {
    await fetchData();
  } catch (e) {
    expect(e).toMatch('error');
  }
});

test('the data is peanut butter', async () => {
  await expect(fetchData()).resolves.toBe('peanut butter');
});

test('the fetch fails with an error', async () => {
  await expect(fetchData()).rejects.toMatch('error');
});