TypeError: AWS.DynamoDB.DocumentClient is not a constructor when testing with Jest

Question

I am running jest tests to test a dynamodb.js file and a create.js file that uses the dynamodb.js file. The create.js module is generic and can insert into any tables by having the param object constructed and passed into it. However, I have been getting the error below and I need help with this.

TypeError: AWS.DynamoDB.DocumentClient is not a constructor

__mock__ folder

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

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

// eslint-disable-next-line func-names
function DynamoDB() {
  return {
    DocumentClient: jest.fn(() => ({
      get: getMock,
      put: putMock
    }))
  };
}

const AWS = { DynamoDB, getMock, putMock };
module.exports = AWS;

dynamodb.js

const AWS = require('aws-sdk');
const http = require('http');
const https = require('https');
const url = require('url');

module.exports = endpoint => {
  const { protocol } = url.parse(endpoint || '');

  const agentConfig = {
    keepAlive: true,
    keepAliveMsecs: 20000
  };

  const httpOptions =
    protocol === 'http:' ? { agent: new http.Agent(agentConfig) } : { agent: new https.Agent(agentConfig) };

  const db = new AWS.DynamoDB({
    endpoint,
    httpOptions
  });

  const docClient = new AWS.DynamoDB.DocumentClient({
    service: db
  });

  return {
    docClient,
    db
  };
};

dynamodb.spec.js

 
const AWS = require('aws-sdk');
const dynamodb = require('../../../src/dynamodb');

describe('dynamodb.js', () => {
  beforeEach(() => {
    // jest.resetModules();
  });

  test('calls generic-dynamodb-lib dynamodb', async () => {
    dynamodb('http://localhost:8001');

    expect(AWS.DynamoDB).toHaveBeenCalled();
    expect(AWS.DynamoDB.DocumentClient).toHaveBeenCalled();
  });
});

create.js

// Imports here

const create = async (log, docClient, table, tableRecord) => {
  try {
    await docClient.put({ TableName: table, Item: tableRecord }).promise();
  } catch (error) {
    log.error({ message: 'DynamoDB error', ...error });
    throw Error.internal();
  }

  return tableRecord;
};

module.exports = create;

I have also tried replacing the manual mock in mock with a doMock block but still continued getting the same error above. Once I get past this, how do I test create.js considering that docClient.js is being passed into the function? Thank you very much.

Answer 1

DocumentClient is supposed to be static property while it was mocked to be instance property.

It should be:

const DynamoDB = jest.fn().mockReturnValue({});
DynamoDB.DocumentClient = jest.fn().mockReturnValue({
  get: getMock,
  put: putMock
});

Answer 2

Thank you very much for your responses. I had already found a way to solve the problem before seeing the response here.

I did not need place any mocks in the __mock__ directory eventually.

Please see the tests that I came up with:

create.spec.js

const AWS = require('aws-sdk');

const dynamodb = require('../../../src/dynamodb');

const create = require('../../../src/create');

describe('create.js', () => {
  beforeEach(() => {
    jest.resetModules();
  });

  test('calls DocumentClient put with a successful outcome', async () => {
    const log = { error: jest.fn() };

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

    AWS.DynamoDB.DocumentClient = jest.fn(() => ({
      put: fakePut
    }));

    const document = {
      brands: ['visa', 'mc', 'amex', 'maestro', 'diners', 'discover', 'jcb']
    };

    const { docClient } = dynamodb('https://localhost:8001');
    await create(log, docClient, 'a-table-name', {
      countryCode: 'US',
      merchantAccount: 'MerchantAccountUS',
      expireAt: 1593814944,
      document
    });

    expect(create).toEqual(expect.any(Function));
    expect(fakePut).toHaveBeenCalled();
    expect(fakePut).toHaveBeenCalledWith({
      TableName: 'a-table-name',
      Item: {
        countryCode: 'US',
        merchantAccount: 'MerchantAccountUS',
        expireAt: 1593814944,
        document
      }
    });
  });

  test('calls DocumentClient put with unsuccessful outcome', async () => {
    const log = { error: jest.fn() };

    const fakePut = jest.fn().mockImplementation(() => {
      throw Error.internal();
    });

    AWS.DynamoDB.DocumentClient = jest.fn(() => ({
      put: fakePut
    }));

    const document = {
      brands: ['visa', 'mc', 'amex', 'maestro', 'diners', 'discover', 'jcb']
    };

    const { docClient } = dynamodb('https://localhost:8001');
    let thrownError;

    try {
      await create(log, docClient, 'a-table-name', {
        countryCode: 'US',
        merchantAccount: 'MerchantAccountUS',
        expireAt: 1593814944,
        document
      });
    } catch (e) {
      thrownError = e;
    }

    expect(create).toEqual(expect.any(Function));
    expect(fakePut).toHaveBeenCalled();
    expect(fakePut).toHaveBeenCalledWith({
      TableName: 'a-table-name',
      Item: {
        countryCode: 'US',
        merchantAccount: 'MerchantAccountUS',
        expireAt: 1593814944,
        document
      }
    });
    expect(thrownError).toEqual(Error.internal());
  });
});

dynamodb.spec.js

const AWS = require('aws-sdk');
const http = require('http');
const https = require('https');
const url = require('url');
const dynamodb = require('../../../src/dynamodb');

const fakeFunction = jest.fn().mockImplementation(() => {});

const FakeDynamoDB = jest.fn(() => ({
  DocumentClient: fakeFunction
}));
AWS.DynamoDB = FakeDynamoDB;

const fakeGet = fakeFunction;
const fakePut = fakeFunction;

const FakeDocumentClient = jest.fn(() => ({
  get: fakeGet,
  put: fakePut
}));
AWS.DynamoDB.DocumentClient = FakeDocumentClient;

describe('dynamodb.js', () => {
  beforeEach(() => {
    jest.resetModules();
  });

  test('calls DynamoDB and DocumentClient constructors with http protocol and with endpoint present', () => {
    const fakeParse = jest.fn().mockImplementation(() => 'http');
    url.parse = fakeParse;

    const fakeHttpAgent = jest.fn().mockImplementation(() => {});
    http.Agent = fakeHttpAgent;

    dynamodb('http://localhost:8001');

    expect(FakeDynamoDB).toHaveBeenCalled();
    expect(FakeDocumentClient).toHaveBeenCalled();
  });

  test('calls DynamoDB and DocumentClient constructors with https protocol and with endpoint present', () => {
    const fakeParse = jest.fn().mockImplementation(() => 'https');
    url.parse = fakeParse;

    const fakeHttpsAgent = jest.fn().mockImplementation(() => {});
    https.Agent = fakeHttpsAgent;

    dynamodb('https://localhost:8001');

    expect(FakeDynamoDB).toHaveBeenCalled();
    expect(FakeDocumentClient).toHaveBeenCalled();
  });
});