Testing an Azure Function in .NET 5

Question

I've started developing Azure Functions and now I want to create my first unit/integration test, but I'm completely stuck. Although I have a very simple Function with an HTTP Trigger and HTTP and Storage Queue output, it seems ridiculously complex te test this.

The code (simplified):

public class MyOutput
{
    [QueueOutput("my-queue-name", Connection = "my-connection")]
    public string QueueMessage { get; set; }

    public HttpResponseData HttpResponse { get; set; }
}

public static class MyFunction
{
    [Function(nameof(MyFunction))]
    public static async Task<MyOutput> Run(
        [HttpTrigger(AuthorizationLevel.Function, "POST")] HttpRequestData req,
        FunctionContext executionContext)
    {
        var logger = executionContext.GetLogger(nameof(MyFunction));
        logger.LogInformation("Received {Bytes} bytes", req.Body.Length);
        //implementation
    }
}

Now I'd expect to build a test like this:

public async Task Test()
{
    var response = await MyFunction.Run(..., ...);
    Assert.IsNotNull(response);
}

After looking hours on the internet to find a good approach, I still didn't find a way to mock HttpRequestData and FunctionContext. I also looked for a full integration test by setting up a server, but this seems really complex. The only thing I ended up was this: https://github.com/Azure/azure-functions-dotnet-worker/blob/72b9d17a485eda1e6e3626a9472948be1152ab7d/test/E2ETests/E2ETests/HttpEndToEndTests.cs

Does anyone have experience testing Azure Functions in .NET 5, who can give me a push in the right direction? Are there any good articles or examples on how to test an Azure Function in dotnet-isolated?

Answer 1

Solution 1

I was finally able to mock the whole thing. Definitely not my best work and can use some refactoring, but at least I got a working prototype:

var serviceCollection = new ServiceCollection();
serviceCollection.AddScoped<ILoggerFactory, LoggerFactory>();
var serviceProvider = serviceCollection.BuildServiceProvider();

var context = new Mock<FunctionContext>();
context.SetupProperty(c => c.InstanceServices, serviceProvider);

var byteArray = Encoding.ASCII.GetBytes("test");
var bodyStream = new MemoryStream(byteArray);

var request = new Mock<HttpRequestData>(context.Object);
request.Setup(r => r.Body).Returns(bodyStream);
request.Setup(r => r.CreateResponse()).Returns(() =>
{
    var response = new Mock<HttpResponseData>(context.Object);
    response.SetupProperty(r => r.Headers, new HttpHeadersCollection());
    response.SetupProperty(r => r.StatusCode);
    response.SetupProperty(r => r.Body, new MemoryStream());
    return response.Object;
});

var result = await MyFunction.Run(request.Object, context.Object);
result.HttpResponse.Body.Seek(0, SeekOrigin.Begin);
var reader = new StreamReader(result.HttpResponse.Body);
var responseBody = await reader.ReadToEndAsync();

Assert.IsNotNull(result);
Assert.AreEqual(HttpStatusCode.OK, result.HttpResponse.StatusCode);
Assert.AreEqual("Hello test", responseBody);

Solution 2

I added the Logger via Dependency Injection and created my own implementations for HttpRequestData and HttpResponseData. This is way easier to re-use and makes the tests itself cleaner.

public class FakeHttpRequestData : HttpRequestData
{
        public FakeHttpRequestData(FunctionContext functionContext, Uri url, Stream body = null) : base(functionContext)
    {
        Url = url;
        Body = body ?? new MemoryStream();
    }

    public override Stream Body { get; } = new MemoryStream();

    public override HttpHeadersCollection Headers { get; } = new HttpHeadersCollection();

    public override IReadOnlyCollection<IHttpCookie> Cookies { get; }

    public override Uri Url { get; }

    public override IEnumerable<ClaimsIdentity> Identities { get; }

    public override string Method { get; }

    public override HttpResponseData CreateResponse()
    {
        return new FakeHttpResponseData(FunctionContext);
    }
}

public class FakeHttpResponseData : HttpResponseData
{
    public FakeHttpResponseData(FunctionContext functionContext) : base(functionContext)
    {
    }

    public override HttpStatusCode StatusCode { get; set; }
    public override HttpHeadersCollection Headers { get; set; } = new HttpHeadersCollection();
    public override Stream Body { get; set; } = new MemoryStream();
    public override HttpCookies Cookies { get; }
}

Now the test looks like this:

// Arrange
var body = new MemoryStream(Encoding.ASCII.GetBytes("{ \"test\": true }"))
var context = new Mock<FunctionContext>();
var request = new FakeHttpRequestData(
                context.Object, 
                new Uri("https://stackoverflow.com"), 
                body);

// Act
var function = new MyFunction(new NullLogger<MyFunction>());
var result = await function.Run(request);
result.HttpResponse.Body.Position = 0;

// Assert
var reader = new StreamReader(result.HttpResponse.Body);
var responseBody = await reader.ReadToEndAsync();
Assert.IsNotNull(result);
Assert.AreEqual(HttpStatusCode.OK, result.HttpResponse.StatusCode);
Assert.AreEqual("Hello test", responseBody);