How to unit test ViewComponent.Invoke()?

Here is just a samle for async,

    [TestMethod]
        public async System.Threading.Tasks.Task InvokeAsyncNameAsync()
{
# setup mocks
...
var httpContext = new DefaultHttpContext();
            var viewContext = new ViewContext();
            viewContext.HttpContext = httpContext;
            var viewComponentContext = new ViewComponentContext();
            viewComponentContext.ViewContext = viewContext;

            var footerComponent = CreateComponentInstance();
            footerComponent.ViewComponentContext = viewComponentContext;

            ViewViewComponentResult result = await footerComponent.InvokeAsync() as ViewViewComponentResult;
            FooterModel resultModel = (FooterModel)result.ViewData.Model;

....
# do your asserts verifications

            Assert.AreEqual(expectedTest, resultModel.FooterText);
}

According to source code the ViewComponent relies on the ViewComponentContext.ViewContext to expose those read only properties, Which in turn accesses the HttpContext. That is your entry point to mock the desired values.

[TestMethod]
public void UserSummaryVcTest() {

    // Arrange
    var expected = "Username value";
    var httpContext = new DefaultHttpContext(); //You can also Mock this
    //...then set user and other required properties on the httpContext as needed

    var viewContext = new ViewContext();
    viewContext.HttpContext = httpContext;
    var viewComponentContext = new ViewComponentContext();
    viewComponentContext.ViewContext = viewContext;

    var viewComponent = new UserSummaryViewComponent();
    viewComponent.ViewComponentContext = viewComponentContext;

    //Act
    var model = viewComponent.Invoke().ViewData.Model as SummaryViewModel;

    //Assert
    Assert.AreEqual(expected, model.UserName);
}