aws-sdk-client-mock

What is aws-sdk-client-mock?

The aws-sdk-client-mock package is a mocking library for AWS SDK v3 clients. It allows developers to mock AWS SDK v3 client methods for unit testing purposes, making it easier to test code that interacts with AWS services without making actual calls to AWS.

What are aws-sdk-client-mock's main functionalities?

Mocking AWS SDK v3 Client Methods

This feature allows you to mock methods of AWS SDK v3 clients. In the example, the S3Client's GetObjectCommand is mocked to return 'mocked data' instead of making an actual call to AWS S3.

const { mockClient } = require('aws-sdk-client-mock');
const { S3Client, GetObjectCommand } = require('@aws-sdk/client-s3');

const s3Mock = mockClient(S3Client);
s3Mock.on(GetObjectCommand).resolves({ Body: 'mocked data' });

async function getObject() {
  const client = new S3Client();
  const command = new GetObjectCommand({ Bucket: 'example-bucket', Key: 'example-key' });
  const response = await client.send(command);
  return response.Body;
}

getObject().then(data => console.log(data));

Resetting Mocks

This feature allows you to reset the mocks, which is useful for cleaning up between tests. In the example, the mock for GetObjectCommand is reset, so any subsequent calls will not use the mock.

const { mockClient } = require('aws-sdk-client-mock');
const { S3Client, GetObjectCommand } = require('@aws-sdk/client-s3');

const s3Mock = mockClient(S3Client);
s3Mock.on(GetObjectCommand).resolves({ Body: 'mocked data' });

// Reset the mock
s3Mock.reset();

async function getObject() {
  const client = new S3Client();
  const command = new GetObjectCommand({ Bucket: 'example-bucket', Key: 'example-key' });
  try {
    const response = await client.send(command);
    return response.Body;
  } catch (error) {
    console.error('Error:', error);
  }
}

getObject();

Mocking Multiple Commands

This feature allows you to mock multiple commands for a single AWS SDK v3 client. In the example, both GetObjectCommand and PutObjectCommand are mocked with different responses.

const { mockClient } = require('aws-sdk-client-mock');
const { S3Client, GetObjectCommand, PutObjectCommand } = require('@aws-sdk/client-s3');

const s3Mock = mockClient(S3Client);
s3Mock.on(GetObjectCommand).resolves({ Body: 'mocked get data' });
s3Mock.on(PutObjectCommand).resolves({ ETag: 'mocked-etag' });

async function performS3Operations() {
  const client = new S3Client();
  const getObjectCommand = new GetObjectCommand({ Bucket: 'example-bucket', Key: 'example-key' });
  const putObjectCommand = new PutObjectCommand({ Bucket: 'example-bucket', Key: 'example-key', Body: 'data' });
  const getObjectResponse = await client.send(getObjectCommand);
  const putObjectResponse = await client.send(putObjectCommand);
  return { getObjectResponse, putObjectResponse };
}

performS3Operations().then(data => console.log(data));

Other packages similar to aws-sdk-client-mock

aws-sdk-mock

aws-sdk-mock is a popular library for mocking AWS SDK v2 methods. It provides similar functionality to aws-sdk-client-mock but is designed for AWS SDK v2. It allows developers to mock AWS service methods for unit testing purposes.

mock-aws-s3

mock-aws-s3 is another library for mocking AWS S3 methods. It is designed to work with AWS SDK v2 and provides a way to mock S3 interactions for testing purposes. It is similar to aws-sdk-client-mock but focused solely on S3.

README

AWS SDK v3 Client mock

Easy and powerful mocking of AWS SDK v3 Clients.

Library recommended by the AWS SDK for JavaScript team - see the introductory post on the AWS blog.

Features:

• 🌊  fluent interface - declaring behavior is short and readable
• 🔍  matching options - defining mock behavior by Command type and/or its input payload
• 🕵️  spying - checking if Commands were actually send
• 🖋️  fully typed - same type control for declaring mock's behavior as when writing regular code
• ✅  fully tested - reliable mocks help instead of impeding

In action:

Table of Contents

• About AWS SDK v3
• Usage
  • Install
  • Import
  • Mock
    • DynamoDB DocumentClient
    • Lib Storage Upload
    • Paginated operations
  • Inspect
• API Reference
• AWS Lambda example
• Caveats
  • Mixed @aws-sdk/types versions
  • Order of mock behaviors
  • Order of type and instance mocks

About AWS SDK v3

The AWS SDK for JavaScript version 3, is the new version of SDK to use in Node.js and browser. It comes with modular architecture and improved typing, thanks to being written in TypeScript.

The recommended way of using it is to create a Client and use it to send Commands.

For example, using SNS Client to publish a message to a topic looks like that:

import {PublishCommand, SNSClient} from '@aws-sdk/client-sns';

const sns = new SNSClient({});
const result = await sns.send(new PublishCommand({
  TopicArn: 'arn:aws:sns:us-east-1:111111111111:MyTopic',
  Message: 'My message',
}));

console.log(`Message published, id: ${result.MessageId}`);

This library provides an easy way to mock sending Commands and define returned results depending on the Command type and payload.

Usage

Install

yarn add -D aws-sdk-client-mock

or

npm install -D aws-sdk-client-mock

With npm, peer dependencies will be installed, including aws-crt. It requires cmake installed locally. You can install it with brew install cmake or similar. See full explanation here.

Import

CommonJS:

const {mockClient} = require('aws-sdk-client-mock');

TypeScript / ES6:

import {mockClient} from 'aws-sdk-client-mock';

Mock

Create mock for all instances or for given instance of the AWS SDK Client:

const snsMock = mockClient(SNSClient);

const dynamoDB = new DynamoDBClient({});
const dynamoDBMock = mockClient(dynamoDB);

By default, mocked Client#send() method returns undefined.

Using the obtained mock instance, you can specify the mock behavior on receiving various commands to send.

Specify default mock behavior:

snsMock.onAnyCommand().resolves({});

// same as:

snsMock.resolves({});

Specify mock behavior on receiving given command only:

snsMock
    .on(PublishCommand)
    .resolves({
        MessageId: '12345678-1111-2222-3333-111122223333',
    });

Specify mock behavior on receiving given command with given payload only:

snsMock
    .on(PublishCommand, {
        TopicArn: 'arn:aws:sns:us-east-1:111111111111:MyTopic',
        Message: 'My message',
    })
    .resolves({
        MessageId: '12345678-4444-5555-6666-111122223333',
    });

Not all payload parameters must be defined to match (you can force strict matching by passing third param strict: true):

snsMock
    .on(PublishCommand, {
        Message: 'My message',
    })
    .resolves({
        MessageId: '12345678-4444-5555-6666-111122223333',
    });

Specify mock behavior on receiving given payload only:

snsMock
    .onAnyCommand({
        TopicArn: 'arn:aws:sns:us-east-1:111111111111:MyTopic',
        Message: 'My message',
    })
    .resolves({
        MessageId: '12345678-4444-5555-6666-111122223333',
    });

Multiple behaviors (for different commands and payloads) may be specified for a single mock:

snsMock
    .resolves({ // default for any command
        MessageId: '12345678-1111-2222-3333-111122223333'
    })
    .on(PublishCommand)
    .resolves({ // default for PublishCommand
        MessageId: '12345678-4444-5555-6666-111122223333'
    })
    .on(PublishCommand, {
        TopicArn: 'arn:aws:sns:us-east-1:111111111111:MyTopic',
        Message: 'My message',
    })
    .resolves({ // for PublishCommand with given input
        MessageId: '12345678-7777-8888-9999-111122223333',
    });

Specify mock throwing an error:

snsMock
    .rejects('mocked rejection');

Specify custom mock function:

snsMock
    .callsFake(input => {
        if (input.Message === 'My message') {
            return {MessageId: '12345678-1111-2222-3333-111122223333'};
        } else {
            return {MessageId: '12345678-4444-5555-6666-111122223333'};
        }
    });

DynamoDB DocumentClient

You can mock the DynamoDBDocumentClient just like any other Client:

import {DynamoDBDocumentClient, QueryCommand} from '@aws-sdk/lib-dynamodb';

const ddbMock = mockClient(DynamoDBDocumentClient);
ddbMock.on(QueryCommand).resolves({
    Items: [{pk: 'a', sk: 'b'}],
});

Lib Storage Upload

To mock @aws-sdk/lib-storage Upload you need to call a helper function mockLibStorageUpload() that will configure required S3Client command mocks:

import {mockLibStorageUpload} from 'aws-sdk-client-mock';
import {Upload} from '@aws-sdk/lib-storage';
import {S3Client} from '@aws-sdk/client-s3';

const s3Mock = mockClient(S3Client);
mockLibStorageUpload(s3Mock);

const s3Upload = new Upload({
    client: new S3Client({}),
    params: {
        Bucket: 'mock',
        Key: 'test',
        Body: 'x'.repeat(6 * 1024 * 1024), // 6 MB
    },
});

s3Upload.on('httpUploadProgress', (progress) => {
    console.log(progress);
});

await s3Upload.done();

You can call mockLibStorageUpload() without providing an S3Client mock. In that case, the client mock will be created and returned from the function. However, you still need to have @aws-sdk/client-s3 installed as a dependency.

Paginated operations

To mock a paginated operation results, simply mock the corresponding Command:

import {DynamoDBClient, paginateQuery, QueryCommand} from '@aws-sdk/client-dynamodb';
import {marshall} from '@aws-sdk/util-dynamodb';

const dynamodbMock = mockClient(DynamoDBClient);
dynamodbMock.on(QueryCommand).resolves({
    Items: [
        marshall({pk: 'a', sk: 'b'}),
        marshall({pk: 'c', sk: 'd'}),
    ],
});

const dynamodb = new DynamoDBClient({});
const paginator = paginateQuery({client: dynamodb}, {TableName: 'mock'});

const items = [];
for await (const page of paginator) {
    items.push(...page.Items || []);
}

Inspect

Inspect received calls:

snsMock.calls(); // all received calls
snsMock.call(0); // first received call

Get calls of a specified command:

snsMock.commandCalls(PublishCommand)

Get calls of a specified command with given payload (you can force strict matching by passing third param strict: true):

snsMock.commandCalls(PublishCommand, {Message: 'My message'})

Under the hood, the library uses Sinon.js stub. You can get the stub instance to configure and use it directly:

const snsSendStub = snsMock.send;

API Reference

See the full API Reference.

AWS Lambda example

Example below uses Jest as a test framework, but mocks will work with any testing library.

Let's take a simple Lambda function that takes a list of messages, sends them to SNS topic and returns message IDs:

import {PublishCommand, SNSClient} from '@aws-sdk/client-sns';

const snsTopicArn = process.env.SNS_TOPIC_ARN || '';

const sns = new SNSClient({});

export const handler = async (event: Event): Promise<string[]> => {
  const promises = event.messages.map(async (msg, idx) => {
    const publish = await sns.send(new PublishCommand({
      TopicArn: snsTopicArn,
      Message: msg,
    }));
    return publish.MessageId!;
  });

  return await Promise.all(promises);
};

interface Event {
  messages: string[];
}

Then the tests could look like this:

import {mockClient} from 'aws-sdk-client-mock';
import {PublishCommand, SNSClient} from '@aws-sdk/client-sns';
import {handler} from '../src';

const snsMock = mockClient(SNSClient);

/**
 * To be sure that unit tests are independent from each other,
 * reset mock behavior between the tests.
 */
beforeEach(() => {
  snsMock.reset();
});

it('message IDs are returned', async () => {
  snsMock.on(PublishCommand).resolves({
    MessageId: '12345678-1111-2222-3333-111122223333',
  });

  const result = await handler({
    messages: ['one', 'two', 'three']
  });

  expect(result).toHaveLength(3);
  expect(result[0]).toBe('12345678-1111-2222-3333-111122223333');
});

it('SNS Client is called', async () => {
  snsMock.on(PublishCommand).resolves({
    MessageId: '111-222-333',
  });

  await handler({
    messages: ['qq', 'xx']
  });

  expect(snsMock.calls()).toHaveLength(2);
});

For more examples, see the unit tests.

Caveats

Mixed @aws-sdk/types versions

If you have multiple @aws-sdk packages in dependencies in different versions, or one of your dependencies depends on the @aws-sdk package(s) in a different version than the one you use, you may end up with different @aws-sdk/types dependency versions required.

If the one installed on the top level in node_modules is in a different version than required by the Client you try to mock, the types will be incompatible. This is because the mocking library will use the @aws-sdk/types version from the top level of node_modules, while your Client may be using a different one.

This often results in a long error stack trace looking similar to this:

Argument of type 'typeof SomeCommand' is not assignable to parameter of type 'new (input: SomeCommandInput) => AwsCommand<SomeCommandInput, MetadataBearer, any, any>'
  Types of construct signatures are incompatible.
    Type 'new (input: SomeCommandInput) => SomeCommand' is not assignable to type 'new (input: SomeCommandInput) => AwsCommand<SomeCommandInput, MetadataBearer, any, any>'.
      Construct signature return types 'SomeCommand' and 'AwsCommand<SomeCommandInput, MetadataBearer, any, any>' are incompatible.
        The types of 'middlewareStack.concat' are incompatible between these types.
          Type '<InputType extends SomeCommandInput, OutputType extends SomeCommandOutput>(from: MiddlewareStack<InputType, OutputType>) => MiddlewareStack<...>' is not assignable to type '<InputType extends SomeCommandInput, OutputType extends MetadataBearer>(from: MiddlewareStack<InputType, OutputType>) => MiddlewareStack<...>'.
            Types of parameters 'from' and 'from' are incompatible.
              Type 'MiddlewareStack<InputType, OutputType>' is not assignable to type 'MiddlewareStack<InputType, SomeCommandOutput>'.
                Types of property 'addRelativeTo' are incompatible.
                  Type '(middleware: MiddlewareType<InputType, OutputType>, options: RelativeMiddlewareOptions) => void' is not assignable to type '(middleware: MiddlewareType<InputType, SomeCommandOutput>, options: RelativeMiddlewareOptions) => void'.
                    Types of parameters 'middleware' and 'middleware' are incompatible.
                      Type 'MiddlewareType<InputType, SomeCommandOutput>' is not assignable to type 'MiddlewareType<InputType, OutputType>'.
                        Type 'InitializeMiddleware<InputType, SomeCommandOutput>' is not assignable to type 'MiddlewareType<InputType, OutputType>'.
                          Type 'InitializeMiddleware<InputType, SomeCommandOutput>' is not assignable to type 'InitializeMiddleware<InputType, OutputType>'.
                            Call signature return types 'InitializeHandler<InputType, SomeCommandOutput>' and 'InitializeHandler<InputType, OutputType>' are incompatible.
                              Type 'Promise<InitializeHandlerOutput<SomeCommandOutput>>' is not assignable to type 'Promise<InitializeHandlerOutput<OutputType>>'.
                                Type 'InitializeHandlerOutput<SomeCommandOutput>' is not assignable to type 'InitializeHandlerOutput<OutputType>'.
                                  Types of property 'output' are incompatible.
                                    Type 'SomeCommandOutput' is not assignable to type 'OutputType'.
                                      'SomeCommandOutput' is assignable to the constraint of type 'OutputType', but 'OutputType' could be instantiated with a different subtype of constraint 'MetadataBearer'.

This is a common problem when using the Amplify library.

The solution for this is to force the version of the @aws-sdk/types matching your Clients to be installed on the top-level of node_modules.

The easiest way to do this is to add the @aws-sdk/types in the selected version to package.json explicitly.

However, depending on your project structure, you may need to force it differently. For example, when using yarn, you can add the @aws-sdk/types in selected version to the resolutions section in package.json.

Order of mock behaviors

Wider Command matchers must be declared first, otherwise, they will take precedence over previous ones.

In this case, all PublishCommand sends will return message ID 222:

snsMock
  .on(PublishCommand, myInput).resolves({MessageId: '111'})
  .on(PublishCommand).resolves({MessageId: '222'});

If the order of the declarations is switched, sends with input matching myInput will return ID 111 and all others 222.

It works similarly with onAnyCommand().

Order of type and instance mocks

When you create both a Client type mock and a specific Client instance mock(s), you need to declare type mock last. Otherwise, the other instances will not be mocked.

Right now if you create a mock for the Client type, and then mock a specific instance of this Client, with the order of mocking as here:

const sns1 = new SNSClient({}); // not mocked

mockClient(SNSClient).resolves({MessageId: '123'});

const sns2 = new SNSClient({}); // mocked
mockClient(sns2).resolves({MessageId: '456'});

const sns3 = new SNSClient({}); // not mocked

Declaring mocks in this order will fix it:

const sns1 = new SNSClient({}); // mocked - default

const sns2 = new SNSClient({}); // mocked
mockClient(sns2).resolves({MessageId: '456'});

mockClient(SNSClient).resolves({MessageId: '123'});

const sns3 = new SNSClient({}); // mocked - default

PRs to fix this are welcome.

Using with Mocha

When testing with Mocha, call mockClient() in the beforeEach() method, not in the global scope, to prevent overriding the mock between test files. See this for more details.

Changelog

0.6.1 (2022-03-05)

Bug Fixes

• bump typescript to 4.6.2 (5c29961), closes #79