Populate IConfiguration for unit tests

Question

.NET Core configuration allows so many options to add values (environment variables, json files, command line args).

I just can't figure out and find an answer how to populate it via code.

I am writing unit tests for extension methods to configurations and I thought populating it in the unit tests via code would be easier than loading dedicated json files for each test.

My current code:

[Fact]
public void Test_IsConfigured_Positive()
{

  // test against this configuration
  IConfiguration config = new ConfigurationBuilder()
    // how to populate it via code
    .Build();

  // the extension method to test
  Assert.True(config.IsConfigured());

}

Update:

One special case is the "empty section" which would look like this in json.

{
  "MySection": {
     // the existence of the section activates something triggering IsConfigured to be true but does not overwrite any default value
   }
 }

---

Update 2:

As Matthew pointed out in the comments having an empty section in the json gives the same result as not having the section at all. I distilled an example and yes, that is the case. I was wrong expecting a different behaviour.

So what do I do and what did I expect:

I am writing unit tests for 2 extension methods for IConfiguration (actually because the binding of values in Get...Settings method does not work for some reason (but thats a different topic). They look like this:

public static bool IsService1Configured(this IConfiguration configuration)
{
  return configuration.GetSection("Service1").Exists();
}

public static MyService1Settings GetService1Settings(this IConfiguration configuration)
{
  if (!configuration.IsService1Configured()) return null;

  MyService1Settings settings = new MyService1Settings();
  configuration.Bind("Service1", settings);

  return settings;
}

My missunderstanding was that if I place an empty section in the appsettings the IsService1Configured() method would return true (which is obviously wrong now). The difference I expected is with having an empty section now the GetService1Settings() method returns null and not as I expected the MyService1Settings with all default values.

Fortunately this still works for me since I won't have empty sections (or now know that I have to avoid those cases). It was just one theoretical case I came across while writing the unit tests.

Further down the road (for those interested in).

For what do I use it? Configuration based service activation/deactivation.

I have an application which has a service / some services compiled into it. Depending on the deployment I need to activate/deactivate the services completly. This is because some (local or testings setups) do not have full access to a complete infrastructure (helper services like caching, metrics...). And I do that via the appsettings. If the service is configured (the config section exists) it will be added. If the config section is not present it will not be used.

---

The full code for the distilled example is below.

• in Visual Studio create a new API named WebApplication1 from the templates (without HTTPS and Authentication)
• delete the Startup class and appsettings.Development.json
• replace the code in Program.cs with the code below
• now in appsettings.json you can activate/deactivate the services by adding/removing Service1 and Service2 section

using Microsoft.AspNetCore;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;
using System;

namespace WebApplication1
{

  public class MyService1Settings
  {
  public int? Value1 { get; set; }
  public int Value2 { get; set; }
  public int Value3 { get; set; } = -1;
  }

  public static class Service1Extensions
  {

  public static bool IsService1Configured(this IConfiguration configuration)
  {
  return configuration.GetSection("Service1").Exists();
  }

  public static MyService1Settings GetService1Settings(this IConfiguration configuration)
  {
  if (!configuration.IsService1Configured()) return null;

  MyService1Settings settings = new MyService1Settings();
  configuration.Bind("Service1", settings);

  return settings;
  }

  public static IServiceCollection AddService1(this IServiceCollection services, IConfiguration configuration, ILogger logger)
  {

  MyService1Settings settings = configuration.GetService1Settings();

  if (settings == null) throw new Exception("loaded MyService1Settings are null (did you forget to check IsConfigured in Startup.ConfigureServices?) ");

  logger.LogAsJson(settings, "MyServiceSettings1: ");

  // do what ever needs to be done

  return services;
  }

  public static IApplicationBuilder UseService1(this IApplicationBuilder app, IConfiguration configuration, ILogger logger)
  {

  // do what ever needs to be done

  return app;
  }

  }

  public class Program
  {

    public static void Main(string[] args)
    {
      CreateWebHostBuilder(args).Build().Run();
    }

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
      WebHost.CreateDefaultBuilder(args)
      .ConfigureLogging
        (
        builder => 
          {
            builder.AddDebug();
            builder.AddConsole();
          }
        )
      .UseStartup<Startup>();
      }

    public class Startup
    {

      public IConfiguration Configuration { get; }
      public ILogger<Startup> Logger { get; }

      public Startup(IConfiguration configuration, ILoggerFactory loggerFactory)
      {
      Configuration = configuration;
      Logger = loggerFactory.CreateLogger<Startup>();
      }

      // This method gets called by the runtime. Use this method to add services to the container.
      public void ConfigureServices(IServiceCollection services)
      {

      // flavour 1: needs check(s) in Startup method(s) or will raise an exception
      if (Configuration.IsService1Configured()) {
      Logger.LogInformation("service 1 is activated and added");
      services.AddService1(Configuration, Logger);
      } else 
      Logger.LogInformation("service 1 is deactivated and not added");

      // flavour 2: checks are done in the extension methods and no Startup cluttering
      services.AddOptionalService2(Configuration, Logger);

      services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_2);
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {

      if (env.IsDevelopment()) app.UseDeveloperExceptionPage();

      // flavour 1: needs check(s) in Startup method(s) or will raise an exception
      if (Configuration.IsService1Configured()) {
        Logger.LogInformation("service 1 is activated and used");
        app.UseService1(Configuration, Logger); }
      else
        Logger.LogInformation("service 1 is deactivated and not used");

      // flavour 2: checks are done in the extension methods and no Startup cluttering
      app.UseOptionalService2(Configuration, Logger);

      app.UseMvc();
    }
  }

  public class MyService2Settings
  {
    public int? Value1 { get; set; }
    public int Value2 { get; set; }
    public int Value3 { get; set; } = -1;
  }

  public static class Service2Extensions
  {

  public static bool IsService2Configured(this IConfiguration configuration)
  {
    return configuration.GetSection("Service2").Exists();
  }

  public static MyService2Settings GetService2Settings(this IConfiguration configuration)
  {
    if (!configuration.IsService2Configured()) return null;

    MyService2Settings settings = new MyService2Settings();
    configuration.Bind("Service2", settings);

    return settings;
  }

  public static IServiceCollection AddOptionalService2(this IServiceCollection services, IConfiguration configuration, ILogger logger)
  {

    if (!configuration.IsService2Configured())
    {
      logger.LogInformation("service 2 is deactivated and not added");
      return services;
    }

    logger.LogInformation("service 2 is activated and added");

    MyService2Settings settings = configuration.GetService2Settings();
    if (settings == null) throw new Exception("some settings loading bug occured");

    logger.LogAsJson(settings, "MyService2Settings: ");
    // do what ever needs to be done
    return services;
  }

  public static IApplicationBuilder UseOptionalService2(this IApplicationBuilder app, IConfiguration configuration, ILogger logger)
  {

    if (!configuration.IsService2Configured())
    {
      logger.LogInformation("service 2 is deactivated and not used");
      return app;
    }

    logger.LogInformation("service 2 is activated and used");
    // do what ever needs to be done
    return app;
  }
}

  public static class LoggerExtensions
  {
    public static void LogAsJson(this ILogger logger, object obj, string prefix = null)
    {
      logger.LogInformation(prefix ?? string.Empty) + ((obj == null) ? "null" : JsonConvert.SerializeObject(obj, Formatting.Indented)));
    }
  }

}

Answer 1

You can use MemoryConfigurationBuilderExtensions to provide it via a dictionary.

using Microsoft.Extensions.Configuration;

var myConfiguration = new Dictionary<string, string>
{
    {"Key1", "Value1"},
    {"Nested:Key1", "NestedValue1"},
    {"Nested:Key2", "NestedValue2"}
};

var configuration = new ConfigurationBuilder()
    .AddInMemoryCollection(myConfiguration)
    .Build();

The equivalent JSON would be:

{
  "Key1": "Value1",
  "Nested": {
    "Key1": "NestedValue1",
    "Key2": "NestedValue2"
  }
}

The equivalent Environment Variables would be (assuming no prefix / case insensitive):

Key1=Value1
Nested__Key1=NestedValue1
Nested__Key2=NestedValue2

The equivalent Command Line parameters would be:

dotnet myapp.dll \
  -- \
  --Key1=Value1 \
  --Nested:Key1=NestedValue1 \
  --Nested:Key2=NestedValue2