
http://www.businessinsider.com/the-future-of-mobile-deck-2012-3?utm_source=twbutton&utm_medium=social&utm_campaign=sai

input:required{ border-color:red; } input:optional{ border-color:whitesmoke; }
<input type="text" name="name" id="first-name" placeholder="enter you first name" required />
public class when_a_new_user_registers_with_invalid_data : SpecsFor<MvcWebApp>
{
protected override void Given()
{
SUT.NavigateTo<AccountController>(c => c.Register());
}
protected override void When()
{
SUT.FindFormFor<RegisterModel>()
.Field(m => m.Email).SetValueTo("notanemail")
//.Field(m => m.UserName).SetValueTo("Test User") --Omit a required field.
.Field(m => m.Password).SetValueTo("P@ssword!")
.Field(m => m.ConfirmPassword).SetValueTo("SomethingElse")
.Submit();
}
//...snip...
}