Mock AWS S3 Select Response with Jest and AWS SDK V3

I am using S3 Select to query the CSV file and extract the rows out of it in my nodejs application. How to write a unit test to mock the response of the SelectObjectContentCommand. The response is of type SelectObjectContentCommandOutput

import { SelectObjectContentCommand, S3Client, ExpressionType, FileHeaderInfo } from '@aws-sdk/client-s3';

const s3Client = new S3Client({});

export const getDataUsingS3Select = async (bucketName: string, fileName: string, query: string, params: any) => {
  
  const command = new SelectObjectContentCommand(params);
  const response = await s3Client.send(command);

  if (response.$metadata.httpStatusCode === 200) {
    if (response.Payload) {
      const data = convertDataToJson(response.Payload);
      return data;
    } else {
      console.log(`S3Select did not have payload for ${bucketName}/${fileName}`);
      return [];
    }
  } else {
    console.log(`S3Select did not receive 200 for ${bucketName}/${fileName}. 
    Metadata is ${response.$metadata}`);
    return [];
  }
}

I got this working by using the Symbol.asyncIterator property:

class MockAsyncIterator {
  constructor(readonly chunks: string[]) {
  }

  async* [Symbol.asyncIterator]() {
    for (const c of this.chunks) {
      yield { Records: { Payload: Buffer.from(c, "utf8") } }
    }
  }
}

then, using aws-sdk-client-mock we can test your function like so:

import { mockClient } from "aws-sdk-client-mock";
const s3Mock = mockClient(S3Client);

test("s3 query", async () => {
  s3Mock.on(SelectObjectContentCommand).resolves({
    Payload: new MockAsyncIterator(["column1,column2", "value1,value2"]),
    "$metadata": {
      httpStatusCode: 200
    }
  })

  const query = {
    // query params
  };

  const result = await getDataUsingS3Select("my-bucket", "my.csv", "SELECT * FROM S3Object", query);
  expect(result).toBeDefined();
  // additional checks
});