Mock AWS

Mocking AWS API calls using Sinon

Use either mockService to mock an entire service, or mockMethod to mock just a single method. Both take the AWS service class (e.g. what you get from import S3 from 'aws-sdk/clients/s3') and the method names/name you want mocked. Optionally you can set the specific API version you want, it will default to the latest.

The resulting methods are sinon.spys. You can use them in the usual way in your spec/test assertions. The method also has a property request. This is a sinon.stub. Use it as usual to specify the return value. If you want your test to be asynchronous and pause on the method call then use a Promise as the return value and resolve it later.

The methods will validate the passed parameters against the 'schema' AWS has catching errors early.

import S3 from 'aws-sdk/clients/s3'
import { mockService } from '@mindhive/mock-aws'

const s3 = mockService(S3, ['getObject', 'putObject'])
const image = some.image()
s3.getObject.request.withArgs(sinon.match({ Key: expectedKey }))
  .returnsValue({ Body: image })
const result = await s3.getObject(params).promise()
s3.getObject.should.have.been.calledOnce
result.Body.should.equal(image)

Testing against DynamoDB

This package installs a bin script dynamodb-local-install which will download AWS's DynamoDB Local. This is stored within node_modules so you will need to reinstall should the package be updated. Then you can start a copy of the local server and get a DynamoDB client pointing to that server with dynamodbClientInstance. The instance is created on a free port so you can run tests in parallel across multiple instances of Node.

Note: the local server requires Java to be installed.

givenTableCreated will ensure the table is setup as per the given properties and empty. As createTable and deleteTable can be slow with the local server it will empty the table in a batch operation if the table properties have not changed.

Example:

import dynamodbClientInstance from '@mindhive/mock-aws/dynamodbClientInstance'
import givenTableCreated from '@mindhive/mock-aws/givenTableCreated'
import DynamoDb from 'aws-sdk/clients/dynamodb'

let dynamodb
before(async () => {  // This can be put in a separate module imported by all tests
  // Ensure local server is started before the test runs
  dynamodb = await dynamodbClientInstance()
})

describe('suite', () => {
  it('should work with DynamoDB table', async () => {
    await givenTableCreated({
      TableName: 'foo',
      ...  // As per DynamoDB.createTable in the AWS SDK
    })
    const docClient = new DynamoDb.DocumentClient({ service: dynamodb })
    await docClient.put({...}).promise()
    ...
  })
})

Table definition from CloudFormation template

You can load the DynamoDB table definition directly from your CloudFomration template ensuring your tests match your production setup.

import givenTableCreated from '@mindhive/mock-aws/givenTableCreated'
import loadCfnYaml from '@mindhive/mock-aws/loadCfnYaml'

const template = loadCfnYaml('resources.cfn.yaml')
await givenTableCreated(template.Resources['FooTable'].Properties)

This will also handle some of the differences between AWS::DynamoDB::Table Properties and the properties required by the SDK to create a table.

Single DynamoDB Local instance

Alternatively you can call the bin script dynamodb-local which downloads the server (if not downloaded already) and starts the local server on the (fixed) standard port. dynamodbClientInstance will look on that port first and use it if it exists.