Serverless testing with Mocha

This will briefly guide you on how to carry out testing with serverless lambda.

Installation

The following dependencies is required:

# Install the mocha test framework globally
$ npm i -g mocha

# Install the serverless-mocha-plugin as development dependencies
$ npm i --save-dev serverless-mocha-plugin

$ npm i -g serverless

You might also need to include your AWS_SECRET_ACCESS_KEY and AWS_ACCESS_KEY_ID in your environment.

Add Test Plugin

Once you have the mocha and the plugin installed, then add the following line to your serverless.yml:

# Code not shown due to brevity
functions:
  hello:
    handler: handler.hello

plugins:
  - serverless-mocha-plugin

Run $ sls to see a list of available commands. You should be able to see additional commands available for testing, namely:

1. create test
2. invoke test

Create Test

Let's say you have a handler:

module.exports.hello = (event, context, callback) => {
	// Code not shown due to brevity
}

In order to create a test for hello function, type the following in your terminal:

$ sls create test --function hello
# or short
$ sls create test -f hello

A test folder with the file hello.js will be created.

Run the test

Now you can run the test with the command:

# Invokes the test
$ sls invoke test

Mock Dependencies

If you are using SQS, SNS, or DynamoDB, you can mock them using the library aws-sdk-mock:

const AWS = require('aws-sdk-mock')
 
AWS.mock('DynamoDB', 'putItem', function (params, callback){
  callback(null, "successfully put item in database")
})
 
AWS.mock('SNS', 'publish', 'test-message')
 
/**
    TESTS
**/
 
AWS.restore('SNS', 'publish')