Mock the constructor for AWS.DynamoDB.DocumentClient using jest

Question

I have a function that looks like this:

function connect() {
   const secret = 'secret';
   const key = 'key';
   const region = 'region';
   const client = new AWS.DynamoDB({
      secret,
      key,
      region
   });'
   return new AWS.DynamoDB.DocumentClient({ service: client })
}

I would like to test the function connect. I have mocked the DynamoDB constructor like this:

// See https://stackoverflow.com/questions/47606545/mock-a-dependencys-constructor-jest
jest.mock('aws-sdk', () => {
  const DynamoDB = jest.fn().mockImplementation(() => {
    return {};
  });
  return {
    DynamoDB,
  };
});

However, this means that the DocumentClient constructor fails. How do I mock that as well?

score 4 · Answer 1 · answered Mar 01 '20 at 18:51

4

This worked for me:

const mockDynamoDbPut = jest.fn().mockImplementation(() => {
  return {
    promise() {
      return Promise.resolve({});
    }
  };
});

jest.doMock('aws-sdk', () => {
  return {
    DynamoDB: jest.fn(() => ({
      DocumentClient: jest.fn(() => ({
        put: mockDynamoDbPut
      }))
    }))
  };
});

I hope it's helpful for you too.

Regards,

David.

answered Mar 01 '20 at 18:51

duxtinto

41
1
4

This gives me the error `ConfigError: Missing region in config`. Any ideas would be appreciated! – Conan Oct 27 '20 at 21:20
When that happens to me it is usually related to the mock not working somehow or in the wrong place. That means DocumentClient tries to connect to db instance. – Guilherme Ribeiro Developer Nov 26 '20 at 23:24

score 2 · Answer 2 · answered Sep 07 '19 at 18:06

DocumentClient might call some of the client method, so simply define those methods stub. Say for example, DocumentClient would use batchGetItem, in your code

import AWS from 'aws-sdk';

jest.mock('aws-sdk', () => {
  const DynamoDB = jest.fn().mockImplementation(() => {
    return {
      batchGetItem: jest.fn(),
    };
  });
  return {
    DynamoDB,
  };
});

// you could inspect the mock
console.log(new AWS.DynamoDB({ ... }));

score 0 · Answer 3 · answered Sep 25 '20 at 13:46

Here what worked for me using jest with TypeScript:

// blabla.test.ts
import { DynamoDB } from 'aws-sdk';
import { ConsumerClass } from '../consumer-class';
import { DependencyConsumerClass } from '../dependency-consumer-class';

/*
* Inside consumerClassInstance.save() is calling this.dynamo.putItem({...}).promise();
*/
jest.mock('aws-sdk', () => {
    return {
        DynamoDB: jest.fn(() => {
            return {
                putItem: jest.fn(() => {
                    return {
                        promise: jest.fn(() => true)
                    };
                })
            };
        })
    };
});

test('sample test', async () => {
    const dependencyConsumerClass = new DependencyConsumerClass();
    const consumerClassInstance = new ConsumerClass(dependencyConsumerClass, new DynamoDB());
    
    const result = await consumerClassInstance.save();
    console.log(result);
});

Jose Quijada · Answer 4 · 2020-06-20T10:46:20.013

Jest provides DynamoDB integration for running tests. See this document, look at 3. Configure DynamoDB client:

const {DocumentClient} = require('aws-sdk/clients/dynamodb');

const isTest = process.env.JEST_WORKER_ID;
const config = {
  convertEmptyValues: true,
  ...(isTest && {endpoint: 'localhost:8000', sslEnabled: false, region: 'local-env'})
};

const ddb = new DocumentClient(config);

I guess you can abstract out (if you haven't already) the DynamoDB client configuration into its own module file and export that client so that it can be required elsewhere, and when the running Jest tests the client gets configured to point the mock DynamoDB server/tables that you have set up as per the other steps of the Jest DynamoDB documentation.

It's really good to know that we don't have to write our own helpers to run integration tests (like I've been doing all this time), I would prefer to not use local dynamo server for unit tests. I think we can just use jest.mock('aws-sdk') if using ts-jest because aws-sdk now ships with typescript definitions. — vamsiampolu, Jun 16 '20 at 23:08

Mock the constructor for AWS.DynamoDB.DocumentClient using jest

4 Answers4