How to Mock Aws-Sdk Gem

How to mock aws-sdk gem?

There are a lot of ways to mock requests in the AWS SDK for Ruby. Trevor Rowe recently posted an article on using the SDK's native support for object stubbing, which does not require any external dependencies like Webmock. You can also use tools like VCR (link will send you to another blog post) to build cacheable integration tests; this way you can test against the live service when you want accuracy and avoid hitting network when you want speed.

Regarding the get request on latest/meta-data/iam/security-credentials/, this happens because the SDK is trying to look up credentials, and, if none are provided, it will check if you are running on an EC2 instance as a last resort, causing the SDK to make an extra HTTP request. You can avoid this check by simply providing bogus static credentials, though if you are using something like VCR, you will want to provide valid credentials for the first run. You can read about how to provide static credentials in another blog post that Trevor wrote on credential management (this should also be in the developer guide and SDK documentation).

How to mock aws-sdk gem?

There are a lot of ways to mock requests in the AWS SDK for Ruby. Trevor Rowe recently posted an article on using the SDK's native support for object stubbing, which does not require any external dependencies like Webmock. You can also use tools like VCR (link will send you to another blog post) to build cacheable integration tests; this way you can test against the live service when you want accuracy and avoid hitting network when you want speed.

Regarding the get request on latest/meta-data/iam/security-credentials/, this happens because the SDK is trying to look up credentials, and, if none are provided, it will check if you are running on an EC2 instance as a last resort, causing the SDK to make an extra HTTP request. You can avoid this check by simply providing bogus static credentials, though if you are using something like VCR, you will want to provide valid credentials for the first run. You can read about how to provide static credentials in another blog post that Trevor wrote on credential management (this should also be in the developer guide and SDK documentation).

How do I mock AWS SDK (v2) with rspec?

I had a hard time finding examples mocking AWS resources. I spent a few days figuring it out and wanted to share my results on Stack Overflow for posterity. I used rspec-mocks (doubles & verifying doubles). Here's an example with the communicator.rb example in the question.

communicator_spec.rb:

RSpec.describe Communicator do
  describe "#consume_messages" do
    it "can use rspec doubles & verifying doubles to mock AWS SDK calls" do
      sqs_client = instance_double(Aws::SQS::Client)
      allow(Aws::SQS::Client).to receive(:new).and_return(sqs_client)
      SQSResponse = Struct.new(:messages)
      SQSMessage = Struct.new(:body, :receipt_handle)
      response = SQSResponse.new([SQSMessage.new(File.read('data/expected_body.json'), "receipt_handle")])
      empty_response = SQSResponse.new([])
      allow(sqs_client).to receive(:receive_message).
                            and_return(response, empty_response)
      allow(sqs_client).to receive(:delete_message).and_return(nil)

      Communicator.new.consume_messages
    end
  end
end

How to Stub Responses with ruby Aws::Lambda::Client SDK

By following the code of stub_responses, it brings you to convert_stub. There seems to be three viable options to mock the responses with: Proc, Hashand the else statement.

def convert_stub(operation_name, stub)
  case stub
  when Proc then stub
  when Exception, Class then { error: stub }
  when String then service_error_stub(stub)
  when Hash then http_response_stub(operation_name, stub)
  else { data: stub }
  end
end

source

In the mocking examples below, I have my AWS client setup as such.

aws_credentials = {
    region: 'us-east-1',
    access_key_id: Rails.application.secrets.aws_key,
    secret_access_key: Rails.application.secrets.aws_secret,
    stub_responses: Rails.env.test?
}
LAMBDA_CLIENT = Aws::Lambda::Client.new(aws_credentials)

---

Mocking Aws::Lambda::Types::InvocationResponse

The else statement allows you to essentially return the same object back. So the best way to mock the response, is to utilize the same class that is being used outside of the test environment. Aws::Lambda::Types::InvocationResponse

context do
  before do
    LAMBDA_CLIENT.stub_responses(
        :invoke,
        Aws::Lambda::Types::InvocationResponse.new(
            executed_version: "$LATEST",
            function_error: nil,
            log_result: nil,
            payload: StringIO.new("hello".to_json),
            status_code: 200
        )
    )
  end
  it { ... }
end

---

Mocking the HTTP Response

Following the logic of using a Hash, we need to peak into what http_response_stub does.

def http_response_stub(operation_name, data)
  if Hash === data && data.keys.sort == [:body, :headers, :status_code]
    { http: hash_to_http_resp(data) }
  else
    { http: data_to_http_resp(operation_name, data) }
  end
end

source

Evidently they are looking for a Hash with the following keys [:body, :headers, :status_code]

context do
  before do
    LAMBDA_CLIENT.stub_responses(
        :invoke,
        {
            body: {testing: true}.to_json,
            headers: {},
            status_code: 200
        }
    )
  end

  it { ... }
end

What gem should I use to work with AWS

You may also want to checkout rightaws though unfortunately it doesn't have support for sns either. It was one of the first libraries available and provides support for most of the functionalities. However, fog is releasing new versions more often and is catching up quickly and is a bit more high level. The aws_sdk was only released recently and the main reason to go with it is that it comes from Amazon itself and will likely become the standard. This is why we included it in rubystack. We expect that people will provide higher level libraries that will build on top of it.

How to test AWS S3 get object method ?

You don't need to (and you shouldn't even try) to test #get_object. That is not implemented by your code and you should assume it has been tested and it works. As for you method #import_from_s3, you have two options. You either don't test it since it is just a thin wrapper around #get_object; or you can make assertions/expectations on its return value.

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