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

Answer 1

Would AddInMemoryCollection extension method help?

You can pass a key-value collection into it: IEnumerable<KeyValuePair<String,String>> with the data you might need for a test.

var builder = new ConfigurationBuilder();

builder.AddInMemoryCollection(new Dictionary<string, string>
{
     { "key", "value" }
});

Answer 2

You can use the following technique to mock IConfiguration.GetValue<T>(key) extension method.

var configuration = new Mock<IConfiguration>();
var configSection = new Mock<IConfigurationSection>();

configSection.Setup(x => x.Value).Returns("fake value");
configuration.Setup(x => x.GetSection("MySection")).Returns(configSection.Object);
//OR
configuration.Setup(x => x.GetSection("MySection:Value")).Returns(configSection.Object);

Answer 3

The solution I went for (which answers the question title at least!) is to use a settings file in the solution testsettings.json and set it to "Copy Always".

    private IConfiguration _config;

    public UnitTestManager()
    {
        IServiceCollection services = new ServiceCollection();

        services.AddSingleton<IConfiguration>(Configuration);
    }

    public IConfiguration Configuration
    {
        get
        {
            if (_config == null)
            {
                var builder = new ConfigurationBuilder().AddJsonFile($"testsettings.json", optional: false);
                _config = builder.Build();
            }

            return _config;
        }
    }

Answer 4

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

Answer 5

I prefer not to have my application classes dependent on IConfiguration. Instead I create a configuration class to hold the config, with a constructor that can initialise it from IConfiguration like this:

public class WidgetProcessorConfig
{
    public int QueueLength { get; set; }
    public WidgetProcessorConfig(IConfiguration configuration)
    {
        configuration.Bind("WidgetProcessor", this);
    }
    public WidgetProcessorConfig() { }
}

then in your ConfigureServices, you just have to do:

services.AddSingleton<WidgetProcessorConfig>();
services.AddSingleton<WidgetProcessor>();

and for testing:

var config = new WidgetProcessorConfig
{
    QueueLength = 18
};
var widgetProcessor = new WidgetProcessor(config);