Unit test Azure Event Hub Trigger (Azure Function)

Question

I have an Azure Function which is an EventHub Trigger. The events are being processed in a batch (EventData[]).

[FunctionName("EventHubTriggerCSharp")]
public async Task Run([EventHubTrigger("samples-workitems", Connection = "EventHubConnectionAppSetting")] EventData[] eventHubMessages, ILogger log)
{
    foreach (var message in eventHubMessages)
    {
        log.LogInformation($"C# function triggered to process a message: {Encoding.UTF8.GetString(message.Body)}");
        log.LogInformation($"EnqueuedTimeUtc={message.SystemProperties.EnqueuedTimeUtc}");
        await service.CallAsync(message);
    }
}

I would like to unit test the above method. But not sure how to pass the EventData[] parameter to this method. After searching for a long time and not finding a way I decided to ask this question.

Is it possible to unit test the above method? Maybe atleast be able to verify the service method is being called?

Answer 1

You should be able to construct the array of EventData and pass that to the Run method along with a mock logger instance.

I have used MsTest but it should be the same logic with NUnit.

[TestClass]
public class EventHubTriggerCSharpTests
{
    private readonly Mock<IService> _mockService = new Mock<IService>();
    private readonly Mock<ILogger> _mockLogger = new Mock<ILogger>();

    private EventHubTriggerCSharp _eventHubTriggerCSharp;

    [TestInitialize]
    public void Initialize()
    {
        _eventHubTriggerCSharp = new EventHubTriggerCSharp(_mockService.Object);
    }

    [TestMethod]
    public async Task WhenEventHubTriggersFunction_ThenCallAsyncWithEventHubMessage()
    {
        // arrange
        var data = "some data";

        var eventHubMessages = new List<EventData>
        {
            new EventData(Encoding.UTF8.GetBytes(data))
            {
                SystemProperties = new EventData.SystemPropertiesCollection(1, DateTime.Now, "offset", "partitionKey")
            }
        };

        // act
        await _eventHubTriggerCSharp.Run(eventHubMessages.ToArray(), _mockLogger.Object);

        // assert
        _mockService.Verify(x => x.CallAsync(eventHubMessages[0]));
    }
}

Note: I haven't actually run the test due to an issue with my Visual Studio but hopefully you get the idea.

Answer 2

• Yes, with the below example you can use unit test the Azure Functions.

• Here is the example Test class for the unit test of Azure function.

    {  
        "id": 1,  
        "CustomerName": "Test User",  
        "Country": "India",  
        "JoiningDate": "28-09-2020",  
        "PrimeUser": false  
    }  

• And here is the Example test class for Azure Event hub unit test

 from unittest.mock import MagicMock
    from unittest.mock import patch
    from azure.eventhub.extensions.checkpointstoreblob import BlobCheckpointStore
    from azure.eventhub import PartitionContext, EventData
    import unittest
    class TestStringMethods(unittest.TestCase):
        @patch('azure.eventhub.EventHubConsumerClient.from_connection_string')
        @patch('azure.eventhub.extensions.checkpointstoreblob.BlobCheckpointStore.from_connection_string')
        def test_eventhub_receive_events(self, mock_blob_checkpoint_store, mock_event_hub_consumer_client):
            mock_event_hub_consumer_client.return_value = MagicMock()
            mock_blob_checkpoint_store.return_value = MagicMock()
            def receive(on_event, **kwargs):
                partition_context = MagicMock()
                partition_context.update_checkpoint = MagicMock()
                on_event(partition_context, EventData("test for Mock"))
            mock_event_hub_consumer_client.receive = receive
            with self.assertLogs('myprogram', level='INFO') as assert_execute:
                receive_events(mock_event_hub_consumer_client)
            self.assertIn("Accepting the event", assert_execute.output[0])
    if __name__ == '__main__':
        unittest.main()

• Below are the Microsoft Documents about unit test in Azure functions for further information.

1. Azure Function Unit Test
2. Azure Eventhub Trigger Unit Test
3. Add Unit Tets to Azure Functions