Input:

When a @User(Peter) #ProposeTo another @User(Patty)
        and @User(Peter) #Marry another @User(Patty)
        and @User(Peter) ~Name is ("Peter")
        and @User(Patty) ~Name is ("Patty"),
        @User(Patty) ~LastName should be the same as @User(Peter) ~LastName
        and each @User should have ~Spouse as the other @User
            and should have ~UnMarried as (false)
            and should have ~Age less than (21)

Output:

[Test]
public void When_User_ProposeTo_User()
{
    IUser Peter = ObjectFactory.GetInstance<IUser>();
    IUser Patty = ObjectFactory.GetInstance<IUser>();
    Peter.ProposeTo(Patty);
    Peter.Marry(Patty);
    Peter.Name = "Peter";
    Patty.Name = "Patty";
    Assert.IsTrue(Patty.LastName == Peter.LastName, "Failed: Patty.LastName == Peter.LastName");
    Assert.IsTrue(!Peter.UnMarried, "Failed: !Peter.UnMarried");
    Assert.IsTrue(Peter.Age < 21, "Failed: Peter.Age < 21");
    Assert.IsTrue(!Patty.UnMarried, "Failed: !Patty.UnMarried");
    Assert.IsTrue(Patty.Age < 21, "Failed: Patty.Age < 21");
    Assert.IsTrue(Peter.Spouse == Patty, "Failed: Peter.Spouse == Patty");
    Assert.IsTrue(Patty.Spouse == Peter, "Failed: Patty.Spouse == Peter");
}