Mock HttpRequest in ASP.NET Core Controller

When creating an instance of the controller under test, make sure to assign a HttpContext that contains the required dependencies for the test to be exercised to completion.

You could try mocking a HttpContext and providing that to the controller or just use DefaultHttpContext provided by the framework

//Arrange
var mockedAccessor = new Mock<IAccessor>();
//...setup mockedAccessor behavior

//...

var httpContext = new DefaultHttpContext(); // or mock a `HttpContext`
httpContext.Request.Headers["token"] = "fake_token_here"; //Set header
 //Controller needs a controller context 
var controllerContext = new ControllerContext() {
    HttpContext = httpContext,
};
//assign context to controller
var controller = new PlayersController (mockedAccessor.Object){
    ControllerContext = controllerContext,
};

//Act
var result = controller.Get();

//...

The above assumes you already know how to mock the controller dependencies like IAccessor and was meant to demonstrate how to provide framework specific dependencies needed for the test.