在Jest/NestJS中如何mock snowflake-sdk等第三方模块？

你的测试代码存在4个核心错误，共同导致了超时问题：

• execute方法入参不匹配：原业务代码中connection.execute接收的是包含sqlText和complete回调字段的对象，你mock的方法写了3个独立参数，完全匹配不上调用逻辑
• 没有触发complete回调：export方法返回的Promise完全依赖complete回调触发resolve/reject，你mock的execute只打了日志，根本没调用传入的complete函数，Promise永远处于pending状态，自然会超时
• 缺少destroy方法实现：原业务代码finally块会调用connection.destroy，你mock的connection对象没有这个方法，执行到这一步会抛出未定义错误
• expect语法错误：你已经对snowflakeClient.export加了await，拿到的是普通值而非Promise，再调用.resolves会直接报错

import { SnowflakeClient } from 'src/snowflake/snowflake-client';
import { Test } from '@nestjs/testing';

describe('SnowflakeClient', () => {
  let snowflakeClient: SnowflakeClient;

  beforeEach(async () => {
    const moduleRef = await Test.createTestingModule({
      providers: [SnowflakeClient],
    }).compile();

    snowflakeClient = moduleRef.get<SnowflakeClient>(SnowflakeClient);
  });

  describe('export', () => {
    it('should export a SQL query', async () => {
      // 构造正确的connection mock
      const connectionMock = {
        execute: jest.fn((options) => {
          // 直接调用complete回调，模拟无错误执行场景
          options.complete(null);
        }),
        destroy: jest.fn((callback) => {
          // mock destroy方法无错误
          callback(null);
        })
      };
      // mock getConnection直接返回上面的mock对象
      jest.spyOn(snowflakeClient, 'getConnection').mockReturnValue(connectionMock);
      
      const bucket = 's3://bucketName';
      const filename = '/reports/test.csv';
      const sql = 'select * from customers limit 100';
      // 正确的校验写法，直接验证返回结果
      expect(await snowflakeClient.export(bucket, filename, sql)).toBe(true);
      // 可选：增加调用校验，验证参数是否符合预期
      expect(connectionMock.execute).toHaveBeenCalledWith(expect.objectContaining({
        sqlText: `COPY INTO 's3://bucketName/reports/test.csv' FROM (select * from customers limit 100)`
      }));
      expect(connectionMock.destroy).toHaveBeenCalled();
    });
  });
});

如果需要测试执行报错的场景，只要在mock execute的时候给complete传错误对象即可：

connectionMock.execute.mockImplementation((options) => {
  options.complete(new Error('snowflake execute error'));
});

然后校验Promise是否抛出对应错误即可。

内容的提问来源于stack exchange，提问作者Marcelo Juventino