如何在Jest中通过提取函数或it.each减少测试代码重复？

你的场景既可以用提取辅助函数，也可以用it.each批量生成测试用例，两种方案分别如下：

方案一：提取重复断言到辅助函数 #

把重复的两个断言封装成复用函数，在每个测试用例的错误捕获逻辑中调用即可：

// 定义辅助函数，复用重复断言逻辑
const validateErrorAndFetchNotCalled = (e: Error) => {
  expect(<jest.Mock>fetch).not.toHaveBeenCalled();
  expect(e).toBeInstanceOf(TypeError);
};

// 修改后的测试用例
it('should throw if no args were passed', async () => {
  expect.assertions(3);
  return readPricing().catch((e: Error) => {
    validateErrorAndFetchNotCalled(e);
    expect(e.message).toBe(
      `The 'products' information is required to successfully be able to execute this request.`
    );
  });
});

it('should throw if no product IDs were passed', () => {
  expect.assertions(3);
  const noIdData = {
    products: [{ salesPrice: '60.00' }, { salesPrice: '80.00' }],
  };
  // @ts-expect-error
  return readPricing(noIdData).catch((e: Error) => {
    validateErrorAndFetchNotCalled(e);
    expect(e.message).toBe(`The 'productId' is required to successfully be able to execute this request.`);
  });
});

it('should throw if an empty array of products was passed', () => {
  expect.assertions(3);
  const noIdData = { products: [] };
  return readPricing(noIdData).catch((e: Error) => {
    validateErrorAndFetchNotCalled(e);
    expect(e.message).toBe(
      `The 'products' information is required to successfully be able to execute this request.`
    );
  });
});

方案二：使用it.each批量生成测试用例 #

把测试的核心参数（测试描述、输入数据、预期错误消息）整理成数组，通过it.each遍历生成所有测试用例，彻底消除重复的测试结构：

// 定义测试参数数组：[测试描述, 输入数据, 预期错误消息]
const errorTestCases = [
  [
    'no args were passed',
    undefined,
    `The 'products' information is required to successfully be able to execute this request.`
  ],
  [
    'no product IDs were passed',
    { products: [{ salesPrice: '60.00' }, { salesPrice: '80.00' }] },
    `The 'productId' is required to successfully be able to execute this request.`
  ],
  [
    'an empty array of products was passed',
    { products: [] },
    `The 'products' information is required to successfully be able to execute this request.`
  ]
];

// 使用it.each批量生成测试
it.each(errorTestCases)('should throw if %s', async (_, inputData, expectedMessage) => {
  expect.assertions(3);
  // @ts-expect-error 处理无参数或参数不符合类型的情况
  return readPricing(inputData).catch((e: Error) => {
    expect(<jest.Mock>fetch).not.toHaveBeenCalled();
    expect(e).toBeInstanceOf(TypeError);
    expect(e.message).toBe(expectedMessage);
  });
});

两种方案各有优势：

• 辅助函数适合保留原有测试结构，只消除重复断言的场景；
• it.each适合测试逻辑高度一致的场景，能大幅减少冗余代码。

内容的提问来源于stack exchange，提问作者Kristina