How to inject a service into a constructor when creating a new instance of an object? - unit-testing

Question

The Setup: I've registered a configuration service that pulls data from appsettings.json and it works fine. I also have a controller that uses that service to get settings from that file, again this works like it's supposed to:
public class ApiController : Controller
{
private readonly string _apiUri;
public ApiController(IOptions<Configurator> config)
{
_apiUri = config.Value.ApiSettings.ApiBaseUrl +
config.Value.ApiSettings.ApiVersion;
}
//...
}
Now note, I'm new to automated unit testing and to asp.net core. What I'd like to do is to decouple the ApiController's reliance on the injected service so that I can use a separate XUnit test project to test functions inside the controller, similar to the example in this tutorial.
To do this I created a model and interface representing the ApiSettings section of my appsettings.json file:
"ApiSettings": {
"ApiBaseUrl": "https://example.com/api/",
"ApiVersion": "v1/"
}
The Model:
public class ApiSettings : IApiSettings
{
public string ApiBaseUri { get; set; }
public string ApiVersion { get; set; }
}
The Interface:
public interface IApiSettings
{
string ApiBaseUri { get; set; }
string ApiVersion { get; set; }
}
I then created a class that would be dependent on the service to inject the settings:
public class ApiSettingsBuilder
{
private readonly string _apiUri;
public ApiSettingsBuilder(IOptions<Configurator> config)
{
_apiUri = config.Value.ApiSettings.ApiBaseUrl +
config.Value.ApiSettings.ApiVersion;
}
public string ApiUri { get { return _apiUri; } }
}
The Problem: How do I create an new instance of this class?
public class ApiController : Controller
{
private readonly string _apiUri;
public ApiController()
{
ApiSettingsBuilder builder = new ApiSettingsBuilder(/*What do I do here*/);
_apiUri = builder.ApiUri;
}
public ApiController(IApiSettings settings)
{
//For testing
_apiUri = settings.ApiBaseUrl + settings.ApiVersion;
}
//...
}
Also, I know this is all a bit overkill, but I would still like an answer because It would possibly be useful in other scenarios.

Answer 1

You don't have to create new classes for unit testing purposes, you can mock the interface of your IOptions using appropriate framework, e.g. Moq:
var configurator = new Configurator() { ApiBaseUrl = "abc" };
var mock = new Mock<IOptions<Configurator>>();
mock.Setup(ap => ap.Value).Returns(configurator);
Then you can pass mocked object to your constructor for unit testing:
var controller = new ApiController(mock.Object);