FeedbackFormViewModelTests.cs

[Fact]
public void ShouldValidateFormAndSendFeedback()
{
    // Create stubs for all dependencies and inject them.
    var sender = Substitute.For<ISender>();
    var clock = Substitute.For<IClock>();
    var feedback = new FeedbackViewModel(sender, clock);
    feedback.HasErrors.Should().BeTrue();

    // Emulate user input.
    feedback.Message = "Message!";
    feedback.Title = "Title!";
    feedback.Section = 0;
    feedback.Idea = true;

    // Ensure there is no errors after we 
    // filled up the form properly.
    feedback.HasErrors.Should().BeFalse();
    
    // Emulate button click and ensure that the `Send()` 
    // method of the dependency was called only once.
    feedback.Submit.Execute().Subscribe();
    service.Received(1).Send("Title!", "Message!");
}