How to unit test a lambda function that includes a dynamoDB query

Question

I have a function in my Alexa skill's lambda function that I am trying to do a unit test for using the aws-lambda-mock-context node package. The method I am trying to test includes a call to DynamoDB to check if an item exists in my table.

At the moment, my test immediately fails with CredentialsError: Missing credentials in config. Following this blog, I tried to manually enter my Amazon IAM credentials into a .aws/credentials file. Testing with the credentials leads to the test running for 30+ seconds before timing out, with no success or fail result from DynamoDB. I am not sure where to go from here.

The function I am looking to unit test looks like this:

helper.prototype.checkForItem = function(alexa) {
  var registration_id = 123;
  var params = {
    TableName: 'registrations',
    Key: {
      id: {"N" : registration_id}
    }
  };

  return this.getItemFromDB(params).then(function(data) {
    //...
  }

And the call to DynamoDB:

helper.prototype.getItemFromDB = function(params) {
  return new Promise(function(fulfill, reject) {
    dynamoDB.getItem(params, function(err, data) {
      if (err == null) {
        console.log("fulfilled");
        fulfill(data);
      }
      else {
        console.log("error recieving data " + err);
        reject(null);
      }
    });
  });
}

score 1 · Answer 1 · answered Feb 02 '18 at 02:44

1

if you want to do unit testing you can mock dynamo db endpoint using any mocking library like nock, also you can check fiddler request/ response what your app is making to dynamo db endpoint and then accordingly you can troubleshoot.

answered Feb 02 '18 at 02:44

Roshan Srivastava

466
2
14

score 1 · Accepted Answer · answered Feb 02 '18 at 13:04

You can use SAM Local to test you lambda:

AWS SAM is a fast and easy way of deploying your serverless applications, allowing you to write simple templates to describe your functions and their event sources (Amazon API Gateway, Amazon S3, Kinesis, and so on). Based on AWS SAM, SAM Local is an AWS CLI tool that provides an environment for you to develop, test, and analyze your serverless applications locally before uploading them to the Lambda runtime. Whether you're developing on Linux, Mac, or Microsoft Windows, you can use SAM Local to create a local testing environment that simulates the AWS runtime environment. Doing so helps you address issues such as performance. Working with SAM Local also allows faster, iterative development of your Lambda function code because there is no need to redeploy your application package to the AWS Lambda runtime. For more information, see Building a Simple Application Using SAM Local.

How to unit test a lambda function that includes a dynamoDB query

2 Answers2