How to mock a HttpContext.GetServerVariable() in .NET Core

Question

I'm trying to test below method with NUnit and Moq in .NET Core environment:

[HttpGet]
public async Task<IActionResult> DeviceType()
{
    string deviceIp = HttpContext.GetServerVariable("REMOTE_ADDR");
    var result = await DeviceService.GetTypeForAsync(deviceIp);
    return Ok(result);
}

The problem is mock a HttpContext.GetServerVariable. I've tried to mock context and insert it by ControllerContext:

var actionContext = new Mock<ActionContext>();
var httpContext = new Mock<HttpContext>();
httpContext.Setup(x => x.GetServerVariable(It.IsAny<string>())).Returns("192.168.1.1");
actionContext.Setup(x => x.HttpContext).Returns(httpContext.Object);
//...
var deviceController = new DeviceController();
deviceController.ControllerContext = new ControllerContext(actionContext.Object);

But test not passed and throw an error:

System.NotSupportedException : Unsupported expression: x => x.GetServerVariable(It.IsAny()) Extension methods (here: HttpContextServerVariableExtensions.GetServerVariable) may not be used in setup / verification expressions.

The question is: how to mock HttpContext.GetServerVariable("REMOTE_ADDR")?

If you look at the source code for the extension method, you will see that it gets the variables via the feature collection on the `Features` property. You'd need to provide a mock `IServerVariablesFeature` from there in your `HttpContext`: https://github.com/dotnet/aspnetcore/blob/ee4e9a8293ef7d1f717596bd8fbaa57e20626633/src/Http/Http.Extensions/src/HttpContextServerVariableExtensions.cs#L19-L29 — Martin Costello, Dec 14 '20 at 15:14

CodeCaster · Answer 1 · 2020-12-14T15:28:59.903

As the error indicates, you can't mock an extension method, as that's a static method, not an overridable or implementable instance or interface method.

The method lives in HttpContextServerVariableExtensions, and merely gets the IServerVariablesFeature feature from the context and forwards the call to that implementation.

So, also mock the IServerVariablesFeature and its this[string] indexer, and let that mock's object be returned from your mocked HttpContext.Features.

score 0 · Answer 2 · answered Dec 14 '20 at 15:37

Thanks to great tips from @martin-costello and @codecaster I'm finally able to mock it:

var serverVarsFeature = new Mock<IServerVariablesFeature>();
serverVarsFeature.Setup(x => x["REMOTE_ADDR"]).Returns("192.168.1.1");           
var httpContext = new Mock<HttpContext>();
httpContext.Setup(x => x.Features.Set(serverVarsFeature.Object));
// ...
var deviceController = new DeviceController();
deviceController.ControllerContext = new ControllerContext();
deviceController.ControllerContext.HttpContext = new DefaultHttpContext(httpContext.Object.Features);

How to mock a HttpContext.GetServerVariable() in .NET Core

2 Answers2