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Test Framework for AWS Lambda




Test Framework for AWS Lambda

Build Status Test Coverage Dependabot Status Dependencies NPM Downloads Semantic-Release Gardener

Testing Framework for AWS Lambda. Very useful for integration testing as you can examine how your lambda function executes for certain input and specific environment variables. Tries to model the cloud execution as closely as possible.

What it does

  • Tests are defined as JSON files
  • Test are dynamically evaluated using Chai
  • Lambda functions are executed using Lambda-Wrapper
  • Supports external request mocking using Nock
  • Allows setting of environment variables on a per test granularity
  • Freeze execution to specific timestamp with Timekeeper
  • Mock randomly generated data, so it does not change between test runs.
  • Set lambda timeout (context.getRemainingTimeInMillis())
  • Set test timeout
  • Specify event input
  • Test success and error responses

Example Projects

Example project using js-gardener and lambda-tdd can be found here.

Getting Started

To install run

$ npm install --save-dev lambda-tdd

Initialize Test Runner and Execute

const minimist = require('minimist');
const LambdaTdd = require('lambda-tdd');

  cwd: __dirname,
  verbose: minimist(process.argv.slice(2)).verbose === true,
  timeout: minimist(process.argv.slice(2)).timeout,
  nockHeal: minimist(process.argv.slice(2))['nock-heal']

You can pass an array of test files to the execute() function or a regular expression pattern. By default tests are auto detected. If a pattern is passed in only matching tests are executed.

The example above allows for use of a --filter=REGEX parameter to only execute specific tests.

Note: If you are running e.g. npm t to run your tests you need to specify the filter option with quadruple dashes. Example:

$ npm t -- --filter=REGEX

Test File Example

  "handler": "geoIp",
  "env": {
    "GOOGLE_PROJECT_ID": "123456789"
  "event": {
    "ip": ""
  "nock": {
    "to": {
      "match": "^.*?\"http://ip-api\\.(com|ca):80\".*?$"
  "expect(body)": {
    "to.contain": "\"United States\""
  "timestamp": 1511072994,
  "success": true,
  "lambdaTimeout": 5000,
  "timeout": 5000

More examples can be found here.

Test Runner Options


Type: string Default: process.cwd()

Directory which other defaults are relative to.


Type string Default: lambda-test

Name of this test runner for debug purposes.


Type boolean Default: false

Display console output while running tests. Useful for debugging.


Type integer Default: undefined

Hard overwrite test timeout for all tests.


Type boolean or string Default: false

Set cassette healing flag for underlying node-tdd


Type boolean Default: false

Automatically heals test when possible.


Type: string Default: handler.js

Handler file containing the handler functions (specified in test).


Type: string Default: __cassettes

Folder containing nock recordings.


Type: string Default: env.yml

Specify yaml file containing environment variables. To allow overwriting of existing environment variables prefix with ^. Otherwise an exception is thrown.

Environment variables set by default are AWS_REGION, AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY since these always get set by the AWS Lambda environment.


Type: string Default: env.recording.yml

Similar to envVarYml. Environment variables declared get applied on top of envVarYml iff this is a new test recording.

Great when secrets are needed to record tests, but they should not be committed (recommendation is to git ignore this file).


Type: string Default: ``

Folder containing test files.


Type: array Default: ["aws-sdk"]

List of dependencies that are required to be flushed before test run. Useful if you need to re-initialize a module that automatically picks up environment variables on initialization (e.g. aws-sdk).

The current project files are always flushed between test runs.

This can not be used for natively compiled modules.


Type: boolean Default: false

Remove rawHeaders from recordings automatically when recording.


Type: object Default: {}

Allows definition of custom test file modifiers for expect and event and for cassette recordings (pipe operator).

Default custom modifiers are: toBase64, toGzip and jsonStringify

Test File Format


Type: string Required

The handler inside the handler file, i.e. if handler.js contained

module.exports.returnEvent = (event, context, cb) => cb(null, event);

we would set this to returnEvent.


Type object Default: {}

Contains environment variables that are set for this test. Existing environment variables can be overwritten.


Type unix Default: Unfrozen

Set unix timestamp that test executing will see. Time does not progress if this option is set.


Type string Default: undefined

Seed used for randomly generated bytes. This mocks crypto.randomBytes.


Type boolean Default: false

By default every "random function" is seeded once per test run. When set to true every function is re-seeded for every invocation. Will greatly reduce "randomness" when set to true.


Type integer Default: Mocha Default Timeout

Set custom timeout in ms for lambda execution. Handy e.g. when recording nock requests.


Type object Default: undefined

Event object that is passed to lambda handler.

Custom actions can be applied by using the pipe character, e.g. { "body|JSON.stringify": {...} } could be used to make input more readable. For more examples see tests.


Type integer Default: 300000

Set initial lambda timeout in ms. Exposed in lambda function through context.getRemainingTimeInMillis(). The timeout is not enforced, but progresses as expected unless timestamp option is used.


Type boolean Required

True iff execution is expected to succeed, i.e. no error is passed into callback.

expect, expect(...)

Type array Default: []

Handle evaluation of response or error (uses success flag). Can define target path, e.g. expect(some.path). Can also apply function with e.g. expect(body|JSON.parse). More details on dynamic expect handling below.

response (DEPRECATED)

Type array Default: []

Deprecated. Use "expect" instead. Dynamic expect logic executed against the response string. More details on dynamic expect handling below.


Type array Default: []

Deprecated. Use "expect" instead. Dynamic expect logic executed against the error string. More details on dynamic expect handling below.


Type array Default: []

Deprecated. Use "expect" instead. Dynamic expect logic executed against the response.body string. More details on dynamic expect handling below.

logs, logs(...)

Type array Default: []

Dynamic expect logic executed against the console output. You can use warn, info, error and log to access the different log level with e.g. logs([error]). More details on dynamic expect handling below.


Type array Default: []

Dynamic expect logic executed against the nock recording. More details on dynamic expect handling below. Note that the nock recording must already exist for this check to evaluate correctly.

Important: If you are running into issues with replaying a cassette file you recorded previously, try editing the cassette and stripping information that might change. Also make sure cassette files never expose secret tokens or passwords!


Type: boolean Default: ?

Remove rawHeaders from recordings automatically when recording. Defaults depends on value set in runner options.


Type: array Default: []

Can define the recordings that are allowed to be unmatched.


Type: array Default: []

Can define the recordings that are allowed to be out of order.

Dynamic Expect Logic

Uses Chai Assertion Library syntax written as json. Lets assume we have an output array [1, 2] we want to validate. We can write

const { expect } = require('chai');

expect([1, 2]).to.contain(1);
expect([1, 2]).to.contain(2);

as the following json

  "to.contain()": 1
}, {
  "to": {
    "contain()": 2

Regular expression are supported if the target is a string matching a regular expression.


Contribution / What's next

Currently nothing planned