AWS Greengrass - Unit test components

Question

Hi there,

I am trying to develop unit tests in python language for simple AWS Greengrass components, using pytest framework and simulating a temperature sensor.

The point here is that I have a SonarQube process running right now locally on my computer, and its main purpose is to check both the code quality and the testing coverage. The first task was easy to make it work, but for testing task, I am able to achieve it only if I ignore the AWS parts, but that is not the way I would like to follow, the whole code should be checked.

Is there any guide I might follow in order to achieve it?

Thanks beforehand, looking forward to hearing from you.

Kind regards
Daniel.

Answer

Hi Greg_B,

First of all, thank you very much for your reply, I was able to achieve one unit test publishing a message to AWS Cloudwatch metric by using the AWS Greengrass component SDK, yet I have many doubts maybe you can solve me, since I cannot see how this procedure is actually working.

I am getting a passed test for the one previously indicated,  which its code is attached below:

```python
    def test_ipc_connect(self, mocker):
        ipc_connect = mocker.patch('awsiot.greengrasscoreipc.connect')
        mocker.patch('json.loads', return_value='1')

init_ipc_client()

ret_cpu = publish_message(ipc_connect, aws_cloudwatch_metric_payload("Greengrass-CoreDevice",  
                "System.Cpu.Usage", "hostname", "co2sink-dev-CoreDevice02", get_cpu_usage()), 
                "cloudwatch/metric/put")
        ipc_connect.assert_called_once()

assert ret_cpu == 1
```

But what really worries me is how it works and how the credentials are internally managed by the mock framework. As fas as I concern, the components that are running within the AWS Greengrass software work since it manages everything by using its own credentials giving at the installation process. What is it really being tested? Is it some kind of simulation?

I have a 75% coverage, which is absolutely rather good, but I am quite demanding, so I would like to have a 90% at least, the problem here is I am not able to test all exceptions that the AWS Greengrasas component SDK might throw.

https://imgur.com/k4k0mX0

How can I test those cases? That is to say, the wrong ones (the publish message method is one from your example codes, but modified to fit in my application).

I have tried something like this, but I am sure that is not ok, because in order to achieve the test properly, the exception should be thrown first within the publish_message method:

```python
    def test_get_secret_exception(self, mocker):
        ipc_connect = mocker.patch('awsiot.greengrasscoreipc.connect', side_effect=Exception('mocked exception'))

with pytest.raises(Exception) as e:
            init_ipc_client()

publish_message(ipc_connect, aws_cloudwatch_metric_payload("Greengrass-CoreDevice",
                            "System.Cpu.Usage", "hostname", "co2sink-dev-CoreDevice02", get_cpu_usage()),
                            "cloudwatch/metric/put")
            assert e.type == SystemExit
            assert e.code == 1

ipc_connect.assert_called_once()
```
https://imgur.com/WectiAf

Thanks beforehand, looking forward to hearing from you.

Kind regards.

Daniel.

Answer

Hi Daniel,

Not a guide, but you can find a small Python unit test example here, showing how to mock the IPC: https://github.com/awslabs/aws-greengrass-labs-component-for-home-assistant/blob/main/tests/test_artifacts_secret.py

This is the code under test: https://github.com/awslabs/aws-greengrass-labs-component-for-home-assistant/blob/main/artifacts/secret.py

Beyond the IPC, you can find more Python unit tests in the directory: https://github.com/awslabs/aws-greengrass-labs-component-for-home-assistant/tree/main/tests

And in this project: https://github.com/awslabs/aws-greengrass-labs-component-for-the-things-stack-lorawan/tree/main/tests

Hopefully that is enough to get you going.

AWS Greengrass - Unit test components

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