Fakes.Azure.Functions

Introduction

A class library to assist with creating unit tests for HTTP Triggers in Azure Function Apps using the isolated process model.

Usage

It is quite simple to get started using the Fakes for writing unit tests. Let's say you have a HTTP Trigger function

using System.Net;
using Microsoft.Azure.Functions.Worker;
using Microsoft.Azure.Functions.Worker.Http;
using Microsoft.Extensions.Logging;

namespace MyFunctionApp;

public class MyFunction
{
    private readonly ILogger<MyFunction> _logger;

    public MyFunction(ILogger<MyFunction> logger)
    {
        _logger = logger;
    }

    [Function("MyFunction")]
    public HttpResponseData Run([HttpTrigger(AuthorizationLevel.Anonymous, "get")] HttpRequestData request)
    {
        _logger.LogInformation("C# HTTP trigger function processed a request.");

        var response = request.CreateResponse(HttpStatusCode.OK);
        response.Headers.Add("Content-Type", "text/plain; charset=utf-8");

        response.WriteString("Welcome to Azure Functions!");

        return response;
    }
}

You wish to write a unit test to verify the function returns a HTTP status code OK.

using Fakes.Azure.Functions;
using Microsoft.Azure.Functions.Worker.Http;
using Microsoft.Extensions.Logging;
using MyFunctionApp;
using Moq;
using System.Net;
using Xunit;

namespace MyFunctionApp.Tests;

public class MyFunctionTests
{
    [Fact]
    public void Function_Returns_Ok()
    {
        Mock<ILogger<MyFunction>> logger = new();

        MyFunction functionUnderTest = new(logger.Object);
        FakeHttpRequestData request = new("https://www.contoso.com");
        HttpResponseData response = functionUnderTest.Run(request);

        Assert.Equal(HttpStatusCode.OK, response.StatusCode);
    }
}

If the function to test has a request body, you have two choices:

• Instantiate a FakeHttpRequest object using the constructor overload FakeHttpRequest(string uri, string body)
• Instantiate a FakeHttpRequest object using the static method FakeHttpRequest.CreateInstance<TBody>(string uri, TBody body)

In either case the resulting HttpRequestData instance will have a Body stream populated with the provided content.

Features

The provided functionality is provided as a starting point and will likely cover most situations. However, advanced usage of HTTP triggers may require implementing more properties in FakeHttpRequestData, FakeFunctionContext or FakeHttpResponseData.

Currently the features supported include:

• Request bodies (POST, PUT)
• Cancellation Tokens
• Response bodies
• Headers (Request & Response)

In cases where a feature is not supported, a NotImplementedException will be thrown. Contributing to the Fake implementations is highly encouraged.