使用NSubstitute对ICommand进行单元测试

Question

I have the following ViewModel

public class MyViewModel : IMyViewModel
{
    private readonly IMyModel myMode;
    private ICommand _myCommand;

    public MyViewModel(IMyModel model)
    {
        _model = model;
    }

    public ICommand MyCommand
    {
        get { return _myCommand ?? (_myCommand = new RelayCommand(x => MyMethod())); }
    }

    private void MyMethod()
    {
        _model.SomeModelMethod();
    }
}

where IMyViewModel is defind as

public interface IMyViewModel
{
    ICommand MyCommand { get; }
} 

and my interface for the model is defined as

public interface IMyModel
{
    void SomeOtherCommand();
} 

Now in my unit test (using NSubstitute) I want to check that when MyCommand is invoked my model receives a call to its method SomeModelMethod . I've tried:

[TestMethod]
public void MyViewModel_OnMyCommand_CallsSomeOtherMethodOnModel()
{
   var model = Substitute.For<IMyModel>();
   var viewModel = Substitute.For<IMyViewModel>();

   viewModel.MyCommand.Execute(null);

   model.Received().SomeOtherMethod();
}

but this doesn't currently work. How do I best test that my Model method is called when a command on my ViewModel is invoked?

Answer 1

Not sure why you're mocking IMyViewModel here. You said you wanted to test whether SomeOtherMethod is invoked when you execute the command in MyViewModel .

You shouldn't be mocking the MyViewModel here.

[TestMethod]
public void MyViewModel_OnMyCommand_CallsSomeOtherMethodOnModel()
{
   var model = Substitute.For<IMyModel>();
   var viewModel = new MyViewModel(model);

   viewModel.MyCommand.Execute(null);

   model.Received().SomeOtherMethod();
}

PS: I'm not familiar with nsubstitute. But the idea is still same (you shouldn't mock MyViewModel). Make sure you're using the right methods in nsubstitute.