aws-lambda-test-utils

Testing your AWS Lambda Functions does not need to be difficult or complex.

If you are new to Amazon WebServices Lambda (or need a refresher), please checkout our our
Beginners Guide to AWS Lambda: https://github.com/dwyl/learn-aws-lambda

## Why?

Testing your code is essential everywhere you need reliability.

AWS Lambda has a Testing Console which is a web-based way of invoking your function(s) with a given input and monitoring the result. But this quite slow and cannot be automated (yet).

What?

The simplest possilbe way we could think of for Testing our AWS Lambda functions.

How? (Usage)

install aws-lambda-test-utils from NPM

npm install aws-lambda-test-utils --save-dev

Use in your Tests

Mock Context

An example of using the mockContextCreator in an example test.

'use strict';
var test               = require('tape');
var utils              = require('aws-lambda-test-utils')
var mockContextCreator = utils.mockContextCreator;
var index              = require('./index.js'); // lambda function

var ctxOpts = {
  functionName: 'LambdaTest',
  functionVersion: '1',
  invokedFunctionArn: 'arn:aws:lambda:eu-west-1:655240711487:function:LambdaTest:ci'
};
var testEvent = { key1: 'value1' };

test('LambdaTest', function(t){
  t.test("LambdaTest: returns value when given event with key1 property", function(st) {
    function test(result){
      st.equals(result, "value1")
      st.end();
    };
    var context = mockContextCreator({}, test); // no options and test as the callback
    index.handler(testEvent, context);
  });
  t.test("LambdaTest: returns value when given event with key1 property", function(st) {
    function test(result){
      st.equals(result, "value1")
      st.end();
    };
    var context = mockContextCreator(ctxOpts, test); // context options specified and test as the callback
    index.handler(testEvent, context);
  });
  t.end();
});

Mock Events

This helper can be used to mock event objects created by AWS services like S3, SNS, or DynamoDB.

The following example uses the mockEventCreator to create a mock DynamoDB event.

/* index.js Lambda function  */
  'use strict';

  exports.handler = function(event, context) {
      // receives am event from Dynamo DB
      context.succeed(event.Records.length);
  };

/* index.test.js  */
'use strict';
var test               = require('tape');
var utils              = require('aws-lambda-test-utils')
var mockContextCreator = utils.mockContextCreator;
var mockEventCreator   = utils.mockEventCreator;
var index              = require('./index.js'); // lambda function

var ctxOpts = {
  functionName: 'LambdaTest',
  functionVersion: '1',
  invokedFunctionArn: 'arn:aws:lambda:eu-west-1:655240711487:function:LambdaTest:ci'
};

var testEvent = mockEventCreator.createDynamoDBEvent();

test('LambdaTest', function(t){
  t.test("LambdaTest: returns value when given event with key1 property", function(st) {
    function test(result){
      st.equals(result, 1)
      st.end();
    };
    var context = mockContextCreator(ctxOpts, test); // no options and test as the callback
    index.handler(testEvent, context);
  });
});

Documentation

Lambda Function event & context

Every AWS Lambda function take two parameters event & context

context

The 'context' object has the following form:

{
  //methods
  success,
  done,
  fail,
  getRemainingTimeInMillis,

  //properties
  functionName,
  functionVersion,
  invokedFunctionArn,
  memoryLimitInMB,
  awsRequestId,
  logGroupName,
  logStreamName,
  identity: {
    cognito_identity_id,
    cognito_identity_pool_id
  },
  clientContext: {
    client: {
      installation_id,
      app_title,
      app_version_name,
      app_version_code,
      app_package_name,
      Custom,
    },
    env: {
      platform_version
      platform,
      make,
      model,
      locale,
    }
  }
}

The properties of the context object can be specified in an options parameter to the mockContextCreator function.

Background Reading

TODO

• Add options to customise the event objects created by the mockEventCreator
• Add stubs for AWS SDK methods