How can I mock AWS Service Comprehend with Sinon, aws-sdk-mock?

Question

I'm beginner with mocking in Typescript. I want to mock AWS.Comprehend in my unit test. I have this code with AWS Service Comprehend.

const comprehend = new AWS.Comprehend();

export const handler = async (): Promise<any> => {

const params = {
    JobName: "first-job",
    InputDataConfig: {
        S3Uri: "input_bucket_name",
        InputFormat: "ONE_DOC_PER_FILE"
    },
    OutputDataConfig: {
        S3Uri: "output_bucket_name"
    },
    DataAccessRoleArn: "role_arn"
};

const result = await comprehend.startDominantLanguageDetectionJob(params)
            .promise()
            .catch(error => {
                    throw error;
                }
            );

    return result.JobId;
};

I try to write an unit test for my code.

import { expect } from 'chai';
import * as AWSMock from 'aws-sdk-mock';
import * as AWS from 'aws-sdk';

describe('unitTest', () => {
    before(() => {
        AWSMock.setSDKInstance(AWS);
        AWSMock.mock('Comprehend', 'startDominantLanguageDetectionJob', (params, cb) => {
            cb(null, { jobId: 'test_job_id', JobStatus: 'SUBMITTED' });
        });
    });

    it('should pass', async () => {
        const result = await handler();

        expect(result).to.be.eql('test_job_id');
    });
});

But my code doesn't work. It seems to me that Comprehend is not a mock. And running normal startDominantLanguageDetectionJob not mock. What is my error with using aws-sdk-mock ?

Answer 1

You can use jest.mock(moduleName, factory, options) to mock aws-sdk package, Comprehend class and its instance methods.

Eg

index.ts :

import AWS from 'aws-sdk';

const comprehend = new AWS.Comprehend();

export const handler = async (): Promise<any> => {
  const params = {
    JobName: 'first-job',
    InputDataConfig: {
      S3Uri: 'input_bucket_name',
      InputFormat: 'ONE_DOC_PER_FILE',
    },
    OutputDataConfig: {
      S3Uri: 'output_bucket_name',
    },
    DataAccessRoleArn: 'role_arn',
  };

  const result = await comprehend
    .startDominantLanguageDetectionJob(params)
    .promise()
    .catch((error) => {
      throw error;
    });

  return result.JobId;
};

index.test.ts :

import MockAWS from 'aws-sdk';
import { handler } from './';

jest.mock('aws-sdk', () => {
  const mComprehend = {
    startDominantLanguageDetectionJob: jest.fn().mockReturnThis(),
    promise: jest.fn(),
  };
  return {
    Comprehend: jest.fn(() => mComprehend),
  };
});

describe('61497560', () => {
  afterEach(() => {
    jest.clearAllMocks();
  });
  it('should return job id', async () => {
    const mComprehend = new MockAWS.Comprehend();
    const mResponse = { JobId: 1 };
    (mComprehend.startDominantLanguageDetectionJob().promise as jest.Mocked<any>).mockResolvedValueOnce(mResponse);
    const actual = await handler();
    expect(actual).toBe(1);
    expect(mComprehend.startDominantLanguageDetectionJob).toBeCalledWith({
      JobName: 'first-job',
      InputDataConfig: {
        S3Uri: 'input_bucket_name',
        InputFormat: 'ONE_DOC_PER_FILE',
      },
      OutputDataConfig: {
        S3Uri: 'output_bucket_name',
      },
      DataAccessRoleArn: 'role_arn',
    });
    expect(mComprehend.startDominantLanguageDetectionJob().promise).toBeCalledTimes(1);
  });

  it('should throw error', async () => {
    const mComprehend = new MockAWS.Comprehend();
    const mError = new Error('network');
    (mComprehend.startDominantLanguageDetectionJob().promise as jest.Mocked<any>).mockRejectedValueOnce(mError);
    await expect(handler()).rejects.toThrow('network');
    expect(mComprehend.startDominantLanguageDetectionJob).toBeCalledWith({
      JobName: 'first-job',
      InputDataConfig: {
        S3Uri: 'input_bucket_name',
        InputFormat: 'ONE_DOC_PER_FILE',
      },
      OutputDataConfig: {
        S3Uri: 'output_bucket_name',
      },
      DataAccessRoleArn: 'role_arn',
    });
    expect(mComprehend.startDominantLanguageDetectionJob().promise).toBeCalledTimes(1);
  });
});

unit test results with 100% coverage:

 PASS  stackoverflow/61497560/index.test.ts (10.06s)
  61497560
    ✓ should return job id (8ms)
    ✓ should throw error (2ms)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |     100 |      100 |     100 |     100 |                   
 index.ts |     100 |      100 |     100 |     100 |                   
----------|---------|----------|---------|---------|-------------------
Test Suites: 1 passed, 1 total
Tests:       2 passed, 2 total
Snapshots:   0 total
Time:        11.292s

Answer 2

If I moved const comprehend = new AWS.Comprehend(); into handler():

export const handler = async (): Promise<any> => {
  const comprehend = new AWS.Comprehend();
 // something
}

My test works. How to do this without moving it?