0-IUserSettings and tests.cs

internal interface IUserSettings
{
    Task<bool> GetFlag(string name);
    Task SetFlag(string name, bool value);
}

internal abstract class UserSettingsTestsBase
{
    protected abstract IUserSettings CreateSubject();

    [TestMethod]
    public async Task MyTestMethod()
    {
        var subject = CreateSubject();
        await subject.SetFlag("foo", true);
        var result = await subject.GetFlag("foo");
        Assert.IsTrue(result);
    }
}

1-AzureBlobStorageUserSettings and tests.cs

internal partial class AzureBlobStorageUserSettings : IUserSettings
{
    private readonly HttpClient _httpClient;

    public AzureBlobStorageUserSettings()
    {
        _httpClient = new HttpClient
        {
            BaseAddress = new Uri("http://myproject.azure.com/blobstorage/")
        };
    }

    public async Task<bool> GetFlag(string name)
    {
        var blob = await _httpClient.GetStringAsync(string.Format("settings/{0}", name));
        return blob == bool.TrueString;
    }

    public async Task SetFlag(string name, bool value)
    {
        await _httpClient.PostAsJsonAsync(string.Format("settings/{0}", name), value);
    }
}

#if !INTEGRATION_TESTS
[Ignore]
#endif
[TestClass]
internal class AzureBlobStorageUserSettingsTests : UserSettingsTestsBase
{
    protected override IUserSettings CreateSubject()
    {
        return new AzureBlobStorageUserSettings();
    }
}

2-UserSettingsSimulatorTests1.cs

[TestClass]
internal class UserSettingsSimulatorTests1 : UserSettingsTestsBase
{
    protected override IUserSettings CreateSubject()
    {
        return new UserSettingsSimulator();
    }

    internal class UserSettingsSimulator : IUserSettings
    {
        private readonly Dictionary<string, bool> _flagsByName = new Dictionary<string, bool>();

        public async Task<bool> GetFlag(string name)
        {
            return _flagsByName[name];
        }

        public async Task SetFlag(string name, bool value)
        {
            _flagsByName[name] = value;
        }
    }
}

3-UserSettingsSimulatorTests2.cs

[TestClass]
internal class UserSettingsSimulatorTests2 : UserSettingsTestsBase
{
    private readonly FakeHttpClienthandler _fakeHttpClienthandler;
    private readonly Dictionary<string, bool> _flagsByName = new Dictionary<string, bool>();

    public UserSettingsSimulatorTests2()
    {
        _fakeHttpClienthandler = new FakeHttpClienthandler
        {
            OverrideSendAsync = async (message, token) =>
            {
                var name = message.RequestUri.ToString().Split('/')[1];
                if (message.Method == HttpMethod.Get)
                {
                    return new HttpResponseMessage(HttpStatusCode.OK)
                    {
                        Content = new StringContent(_flagsByName[name].ToString())
                    };
                }

                if (message.Method == HttpMethod.Post)
                {
                    _flagsByName[name] = await message.Content.ReadAsStringAsync() == "true";
                    return new HttpResponseMessage(HttpStatusCode.OK)
                    {
                        Content = new StringContent(_flagsByName[name].ToString())
                    };
                }

                throw new Exception();
            }
        };
    }

    protected override IUserSettings CreateSubject()
    {
        var httpClient = new HttpClient(_fakeHttpClienthandler)
        {
            BaseAddress = new Uri("http://myproject.azure.com/blobstorage/")
        };
        return new AzureBlobStorageUserSettings(httpClient);
    }
}

internal class FakeHttpClienthandler : HttpMessageHandler
{
    public Func<HttpRequestMessage, CancellationToken, Task<HttpResponseMessage>> OverrideSendAsync;

    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request,
        CancellationToken cancellationToken)
    {
        return OverrideSendAsync(request, cancellationToken);
    }
}

internal partial class AzureBlobStorageUserSettings
{
    // only required for UserSettingsSimulatorTests2's FakeHttpClient
    public AzureBlobStorageUserSettings(HttpClient httpClient)
    {
        _httpClient = httpClient;
    }
}