How to pass in settings into a class (derived ASP.NET Core Startup.cs) from ConfigureServices in a test

Question

I basically have this code

[Fact]
public async Task Test()
{
   var settings = new MySettings() { Name = "Jhon" }; //<-- use this

   var webHostBuilder = new WebHostBuilder()
    .UseStartup<TestStartup>()
    .ConfigureServices(services =>
    {
        // this is called...
        services.AddSingleton(settings);
    });
       
     //omitted code.. 
 }

And I want to be able to use MySettings in the TestStartup.

Whatever I try just returns Name == null..

I have tried this

public class TestStartup : Startup
{
    public TestStartup(IConfiguration configuration) : base(configuration)
    {
       Configuration = configuration;

       // Name is always != "Jhon"

       // doesn't work
       var mySettings = configuration.Get<MySettings>();

       // doesn't work either
       var mySettings = new MySettings();
       configuration.Bind("MySettings", mySettings);

       // tried various other things that didn't work
    }
}

What am I missing?

Answer 1

You can leverage the MemoryConfigurationProvider:

using Microsoft.Extensions.Configuration;

var webHostBuilder = new WebHostBuilder()
    .ConfigureAppConfiguration(configurationBuilder => configurationBuilder
        .AddInMemoryCollection(new Dictionary<string, string?>
        {
            { "Name", "Jhon" },
            {"Logging:LogLevel:Default", "Warning"}
        }))
    .UseStartup<TestStartup>()
    // ...

and then it can be consumed with any standard pattern for configuration, for example:

public class TestStartup : Startup
{
    public TestStartup(IConfiguration configuration) : base(configuration)
    {
       var nameKeyValue = Configuration["Name"];
    }
}

If you wanted to pass a whole class over it could be done with this helper

public static class TestHelpers<T> where T : new()
{
    /// <summary>
    /// Helper class to convert an object of type T to a dictionary.
    /// </summary>
    /// <param name="objectToConvert"></param>
    /// <returns></returns>
    public static Dictionary<string, string?> ConvertObjectToDictionary(T objectToConvert)
    {
        var dictionary = new Dictionary<string, string?>();

        foreach (var property in objectToConvert.GetType().GetProperties())
        {
            var value = property.GetValue(objectToConvert);
            dictionary.Add(property.Name, value?.ToString());
        }

        return dictionary;
    }

    /// <summary>
    /// Helper class to convert a dictionary back to an object of type T.
    /// </summary>
    /// <param name="configDictionary"></param>
    /// <returns></returns>
    public static T ConvertDictionaryToObject(Dictionary<string, string> configDictionary)
    {
        var objectToPopulate = new T();
        var properties = objectToPopulate.GetType().GetProperties();

        foreach (var property in properties)
        {
            if (configDictionary.ContainsKey(property.Name))
            {
                var value = configDictionary[property.Name];
                if (value != null)
                {
                    try
                    {
                        property.SetValue(objectToPopulate, Convert.ChangeType(value, property.PropertyType));
                    }
                    catch (Exception ex)
                    {
                        // swallow exception for private properties. This could be logged out
                    }
                }
            }
        }

        return objectToPopulate;
    }
}

and use it like this

var settings = new MySettings() { Name = "Jhon" };

// convert the class to dictionary
var mySettingsDictionary= TestHelpers<MySettings>.ConvertObjectToDictionary(settings);

// and convert it back to class     
var mySettingsClass= TestHelpers<MySettings>.ConvertDictionaryToObject(mySettingsDictionary);

// and in the TestStartup like this
var mySettingsClass= TestHelpers<MySettings>.ConvertDictionaryToObject(Configuration.AsEnumerable().ToDictionary(x => x.Key, x => x.Value))