A object templator for your unittests, like factorygirl

Blueprint.cs

using System;

namespace Blueprint {
    public class Blueprint<T> {
        Func<IdGenerator, T> constructor;

        //IdGenerator is static, so all objects of type T will have a different Id
        private static IdGenerator idgen = new IdGenerator();

        public Blueprint(Func<IdGenerator, T> constructor) {
            this.constructor = constructor;
        }
        
        public Blueprint<T> With(Action<T> modifier) {
            return new Blueprint<T>((idGenParam) => {
                var obj = constructor(idGenParam);
                modifier(obj);
                return obj;
            });
        }

        public T Create() {
            return constructor(idgen);
        }

        public T Create(Action<T> modifier) {
            var o = constructor(idgen);
            modifier(o);
            return o;
        }

    }

    public class IdGenerator {
        private int iter = 0;
        public int Next() {
            return iter++;
        }
    }
}

Blueprintusage.cs

using System;
using System.Linq.Expressions;
using System.Diagnostics;

namespace Blueprint {
    public class Blueprintusage {
        public Blueprintusage() {
            //Blueprint
            var skeet = new Blueprint<Person>((idGen) => new Person {
                //Unique Id's
                Id = idGen.Next(),
                LastName = "Skeet",
            });

            //Override properties
            Blueprint<Person> writerSkeet = skeet.With(p => {
                p.Job = "Writer";
            });

            Blueprint<Person> coderSkeet = skeet.With(p => {
                p.Job = "Coder Extraordinaire";
            });

            //Dynamic properties
            Blueprint<Person> oldWriterSkeet = skeet.With(p => {
                p.Age = (DateTime.Now - new DateTime(1920, 11, 10)).Hours / 365; //Will be evaluated each time when Create is called
            });

            Person someGenericWriterSkeet = writerSkeet.Create();
            Person JohnSkeet = skeet.Create(x => x.FirstName = "Jon");
        }
    }
}

Person.cs

namespace Blueprint {
    public class Person {
        public int Id;
        public string FirstName;
        public string LastName;
        public string Job;
        public int Age;
    }

}