Mocking .Net Core IConfiguration

The appsettings.json configuration can be mocked in several ways, the examples below use Moq.

Consider these settings:

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{
  "Services": {
    "SomeService": {
      "Url": "http://someservice:81"
    }
  }
}

This would be read in the consumer class as:

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var url = config.GetValue<string>("Services:SomeService:Url");

Option 1: Mock configurationSection and configuration

In the testing class you need to mock configurationSection and configuration as follows

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var configurationSectionMock = new Mock<IConfigurationSection>();
var configurationMock = new Mock<IConfiguration>();

configurationSectionMock
   .Setup(x => x.Value)
   .Returns("http://someservice:81");

configurationMock
   .Setup(x => x.GetSection("Services:SomeService:Url"))
   .Returns(configurationSectionMock.Object);

Then inject configurationMock.Object and it will be happy as when config.GetValue is called.

Option 2: Read appsettings file based on Environment

Build up configuration and read appsettings file.

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var environment = Environment.GetEnvironmentVariable("ASPNETCORE_ENVIRONMENT");

var configuration = new ConfigurationBuilder()
    .SetBasePath(Directory.GetCurrentDirectory())
    .AddJsonFile($"appsettings.{environment}.json")
    .Build();

You can now read the configuration from configuration

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var url = configuration.GetValue<string>("Services:SomeService:Url");
var connectionString = configuration.GetConnectionString("FooConnectionString");

Option 3: In Memory Collection

If the settings are nested and you need to mock several you can use a dictionary and add to the builder with .AddInMemoryCollection(appSettingsStub)

Consider these settings, the mock concearned with the RetryCount and RetrySleepDuration

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{
  "Services": {
    "SomeService": {
      "Url": "http://someservice:81",
      "RetryCount": 3,
      "RetrySleepDuration": 2
    }
  }
}

Create the dictionary

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var appSettingsStub = new Dictionary<string, string> {
    {"Services:SomeService:RetryCount", "3"},
    {"Services:SomeService:RetrySleepDuration", "2"}
};

Create the config

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

Using a simple options class

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public class SomeServiceOptions
{
    public const string SomeService = "Services:SomeService";
    public string Url { get; set; }
    public int RetryCount { get; set; }
    public int RetrySleepDuration { get; set; }
}

You can then access this config and bind it to the options class.

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var someServiceConfig = configuration
  .GetSection(SomeServiceOptions.SomeService)
  .Get<SomeServiceOptions>();