Test infrastructure for C# Azure Function testing (#2055)

Add support for function tests and the ability to run them against either real Azure Storage or the Azurite emulator.

See follow-up PR #2032 for actual usage.

src/ApiService/Tests/Fakes/TestHttpRequestData.cs

@@ -0,0 +1,78 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Net;
+using System.Security.Claims;
+using Azure.Core.Serialization;
+using Microsoft.Azure.Functions.Worker;
+using Microsoft.Azure.Functions.Worker.Http;
+using Microsoft.Extensions.Options;
+using Moq;
+
+namespace Tests.Fakes;
+
+sealed class TestHttpRequestData : HttpRequestData {
+    private static readonly ObjectSerializer Serializer =
+        // we must use our shared JsonSerializerOptions to be able to serialize & deserialize polymorphic types
+        new JsonObjectSerializer(Microsoft.OneFuzz.Service.OneFuzzLib.Orm.EntityConverter.GetJsonSerializerOptions());
+
+    sealed class TestServices : IServiceProvider {
+        sealed class TestOptions : IOptions<WorkerOptions> {
+            // WorkerOptions only has one setting: Serializer
+            public WorkerOptions Value => new() { Serializer = Serializer };
+        }
+
+        static readonly IOptions<WorkerOptions> Options = new TestOptions();
+
+        public object? GetService(Type serviceType) {
+            if (serviceType == typeof(IOptions<WorkerOptions>)) {
+                return Options;
+            }
+
+            return null;
+        }
+    }
+
+    private static FunctionContext NewFunctionContext() {
+        // mocking this out at the moment since there’s no way to create a subclass
+        var mock = new Mock<FunctionContext>();
+        var services = new TestServices();
+        mock.SetupGet(fc => fc.InstanceServices).Returns(services);
+        return mock.Object;
+    }
+
+    public static TestHttpRequestData FromJson<T>(string method, T obj)
+        => new(method, Serializer.Serialize(obj));
+
+    public TestHttpRequestData(string method, BinaryData body)
+        : base(NewFunctionContext()) {
+        Method = method;
+        _body = body;
+    }
+
+    private readonly BinaryData _body;
+
+    public override Stream Body => _body.ToStream();
+
+    public override HttpHeadersCollection Headers => throw new NotImplementedException();
+
+    public override IReadOnlyCollection<IHttpCookie> Cookies => throw new NotImplementedException();
+
+    public override Uri Url => throw new NotImplementedException();
+
+    public override IEnumerable<ClaimsIdentity> Identities => throw new NotImplementedException();
+
+    public override string Method { get; }
+
+    public override HttpResponseData CreateResponse()
+        => new TestHttpResponseData(FunctionContext);
+}
+
+sealed class TestHttpResponseData : HttpResponseData {
+    public TestHttpResponseData(FunctionContext functionContext)
+        : base(functionContext) { }
+    public override HttpStatusCode StatusCode { get; set; }
+    public override HttpHeadersCollection Headers { get; set; } = new();
+    public override Stream Body { get; set; } = new MemoryStream();
+    public override HttpCookies Cookies => throw new NotSupportedException();
+}