How to test Lambdas using crhelper

[SchnitzelKopf]

Sorry for this stupid question...

How do I run tests? When using cfnresponse I could simply create a standard Lambda Cloudformation TestEvent and somewhat test my lambda (besides the cfnresponse failing in the end).

When trying the same with a Lambda using crhelper I run into loads of errors as I do not want to specify a CFN Stack to send the response to. I simply want to run my code and not communicate with CFN-Stacks (as there are none so far).

Here is my sample test event which returns this error. Basically it's a createSnapshot for elastiCache, however I don't think this is relevant. The final product would be a CFN Template accessible via ServiceCatalog where customers enter their ReplicationGroupId to create a snapshot.
" socket.gaierror: [Errno -2] Name or service not known[ERROR] Unexpected failure sending response to CloudFormation [Errno -2] Name or service not known "

{ "RequestType": "Create", "ResponseURL": "http://pre-signed-S3-url-for-response", "StackId": "arn:aws:cloudformation:eu-central-1:123456789012:stack/MyStack/guid", "RequestId": "unique id for this create request", "ResourceType": "Custom::TestResource", "LogicalResourceId": "MyTestResource", "ResourceProperties": { "StackName": "MyStack", "ApplicationName": "abcd", "SnapshotMode": "Create", "CacheClusterId": "", "ReplicationGroupId": "abcd-ttwoshards", "CostReference": "abc", "KmsKeyId": "abc", "SnapshotName": "mySnapshotviaLambda" } }

Thanks you for helping a newb out. If this isn't the right place to ask this question please let me know the right place to ask, or link a me docs explaining what I am tryin to achieve.

[nikoizs]

+1. I am encountering a similar situation where I am trying to test my custom resource lambda function locally with local-invoke, I want to be able to return a success in a local test without calling Cloudformation.

[Lewenhaupt]

You should be able to create a mock endpoint for the ResponseURL?

[iainelder]

You don't need to create a stack to test it. (And it's just as well because a broken custom resource lambda can all too easily cause CloudFormation to hang for an hour or more!)

You can do this by mocking the _send method of the CfnResource class. I described it in more detail in #54. Does it help?

Following @Lewenhaupt's suggestion, if you don't mind creating a temporary S3 bucket for the test, then you could just create a bucket and use its URL for your test requests. According to the _send_response function then it should work, but I'll admit I haven't tried this yet.

[mdavis-xyz]

Alternatively if you assume this library is bug-free and you want to test just your own code (e.g. you don't want the library to catch and ignore exceptions during deletion) just use a wrapper.

@helper.create
def create(event, context):
    return _create(event, context)
def _create(event, context=None):
    your code here

Then in your test:

def my_test():
    ret = _create(event)