How to Unit Test Method Calling IConfiguration.Get<T> extension

Question

I have this very simple method that I need to unit test.

public static class ValidationExtensions
{
    public static T GetValid<T>(this IConfiguration configuration)
    {
        var obj = configuration.Get<T>();
        Validator.ValidateObject(obj, new ValidationContext(obj), true);
        return obj;
    }
}

The problem is that configuration.Get<T> is a static extension method and doesn't belong to IConfiguration. I can't change the implementation of that static method.

I'm thinking, perhaps the simplest way is to create a Memory Configuration Provider? But I don't know if I can create one without binding it to a web host.

Answer 1

The configuration module is independent of web host related features.

You should be able to create an in memory configuration to test against without the need to bind it to a web host.

Review the following example test

public class TestConfig {
    [Required]
    public string SomeKey { get; set; }
    [Required] //<--NOTE THIS
    public string SomeOtherKey { get; set; }
}

//...

[Fact]
public void Should_Fail_Validation_For_Required_Key() {
    //Arrange
    var inMemorySettings = new Dictionary<string, string>
    {
        {"Email:SomeKey", "value1"},
        //{"Email:SomeOtherKey", "value2"}, //Purposely omitted for required failure
        //...populate as needed for the test
    };

    IConfiguration configuration = new ConfigurationBuilder()
        .AddInMemoryCollection(inMemorySettings)
        .Build();

    //Act
    Action act = () => configuration.GetSection("Email").GetValid<TestConfig>();

    //Assert
    ValidationException exception = Assert.Throws<ValidationException>(act);
    //...other assertions of validation results within exception object
}

This in my opinion would be coming close to an integration test, but ideally you are just using framework dependent features in order to isolate the testing of the extension method.