Is there's a way to spyOn for aws S3 bucket to test funcionality?

Question

Working with typescript project we are using s3 to save images.

The s3 operations aren't called directly from s3 but a service called FileService that has the basic structure to handle all the basic operations looks like this:

static getSignedUrlFromS3(info: SignedUrlInfo) {
    try {
      return s3.getSignedUrlPromise(info.operationType, {
        Bucket: info.bucket,
        Key: info.key,
        Expires: info.expires,
      });
    } catch (error) {
      winston.error(
        `Error retrieving signed url '${info.key}' from S3 Bucket '${info.bucket}'`,
        error,
      );

      return Promise.resolve();
    }
  }

  /**
   * Get a list of objects from a S3 bucket.
   */
  static getBucketObjectsList(info: ObjectListInfo) {
    try {
      return s3
        .listObjectsV2({
          Bucket: info.bucket,
          Delimiter: info.delimiter,
          Prefix: info.prefix,
        })
        .promise();
    } catch (error) {
      winston.error(
        `Error retrieving object list from S3 Bucket '${info.bucket}'`,
        error,
      );

      return Promise.resolve();
    }

  /**
   * Creates a S3 Presigned Post that for add an object into S3 bucket
   */
  static createS3PresignedPost(info: PresignedUrlInfo) {
    try {
      const params = {
        Bucket: info.bucket,
        Fields: {
          key: info.key,
        },
        Expires: info.expires,
      };

      return s3.createPresignedPost(params);
    } catch (error) {
      winston.error(
        `Error creating presigned POST for S3 Bucket '${info.bucket}'`,
        error,
      );

      return;
    }
  }

So basically I have another Service that consumes this one calling the specific methods of the other service as follow:

static getOne(key: string): Promise<Response> {
    return new Promise(async (resolve, reject) => {
      const signedUrl = await FileService.getSignedUrlFromS3({
        bucket: bucketName,
        operationType: 'getObject',
        key: key,
        expires: 60 * 60 * 24,
      });
      if (typeof signedUrl === 'string') {
        resolve({
          key,
          url: signedUrl,
          date: this._getDateFromKey(key),
        });
      } else {
        winston.error(`Error finding ${bucketName}/${key} in S3`);
        reject(new ServerExceptionBadRequest('Unable to get media file.'));
      }
    });
  }

So my question is how can I mock S3 to simulate the functionality of the services like make a signedPost GetObject, CopyObject etc.

What I have seen in documentation about is something like this:

jest.mock('@aws-sdk/client-s3');

import { VehicleMediaService } from '@api-services/VehicleMediaService';
import {
  MediaStatus,
  MediaType,
} from '@api-services/VehicleMediaService.interfaces';

import * as S3 from '@aws-sdk/client-s3/S3.spec';

const mocked = S3 as jest.Mocked<typeof S3>;

But not quite super sure about how to used. Thank you very much for your help.

Answer 1

The solution is mock the services using the aws-sdk. For example:

jest.spyOn(yourService, 'yourMethod').mockImplementation(() => {
      const response = new Response<S3.Types.ListObjectsV2Output, AWSError>();
       
      const result: PromiseResult<S3.Types.ListObjectsV2Output, AWSError> = {
        $response: response,
        Contents: objectFiles,
      };
      return Promise.resolve(result);
    });

So that way you can mock any aws service.