ContactEditTests.cs

public class ContactEditTests
{
    ...

    public void ShouldRequireMinimumFields()
    {
        new ContactEdit.Command()
            .ShouldNotValidate("'Name' should not be empty.");
    }

    public void ShouldRequireValidEmailWhenProvided(ContactEdit.Command command)
    {
        command.Email = null;
        command.ShouldValidate();

        command.Email = "test@example.com";
        command.ShouldValidate();

        command.Email = "test at example dot com";
        command.ShouldNotValidate("'Email' is not a valid email address.");
    }

    ...
}