From: http://hjerpbakk.com/blog/2013/10/1/async-method-caller-easy-async-without-await.html View the complete code in: https://github.com/Sankra/CSharpExamples

ViewModelWithAsyncMethodCaller.cs

public class ViewModelWithAsyncMethodCaller {
    private readonly AsyncMethodCaller asyncMethodCaller;

    public ViewModelWithAsyncMethodCaller(AsyncMethodCaller asyncMethodCaller) {
        this.asyncMethodCaller = asyncMethodCaller ?? new AsyncMethodCaller();
    }

    public string Message { get; set; }
    public string Result { get; set; }

    public void ExecuteAsync() {
        Message = "Loading...";
        asyncMethodCaller.CallMethodAndContinue(DoSomething, WorkCompleted, HandleError);
    }

    private string DoSomething() {
        return "Result";
    }

    private void WorkCompleted(string result) {
        Message = "Completed";
        Result = result;
    }

    private void HandleError(Exception exception) {
        Message = exception.Message;
    }
}

[TestFixture]
public class ViewModelTests {
    [Test]
    public void DoSomething() {
        var asyncMethodCaller = new TestAsyncMethodCaller();
        var viewModel = new ViewModelWithAsyncMethodCaller(asyncMethodCaller);

        viewModel.ExecuteAsync();

        Assert.AreEqual("Loading...", viewModel.Message);

        asyncMethodCaller.StartServiceAndWait();

        Assert.AreEqual("Result", viewModel.Result);
        Assert.AreEqual("Completed", viewModel.Message);
    }
}