I am embarking upon my first journey of test driven development in C#. To get started I'm using MSTest and Rhino.Mocks. I am attempting to write my first unit tests against my ICustomerRepository. It seems tedious to new up a Customer for each test method. In ruby-on-rails I'd create a seed file and load the customer for each test. It seems logical that I could put this boiler plate Customer into a property of the test class but then I would run the risk of it being modified. What are my options for simplifying this code?

[TestMethod]
public class CustomerTests : TestClassBase
{
    [TestMethod]
    public void CanGetCustomerById()
    {
        // arrange
        var customer = new Customer()
        {
            CustId = 5,
            DifId = "55",
            CustLookupName = "The Dude",
            LoginList = new[] {
                new Login { LoginCustId = 5, LoginName = "tdude" } }
        };

        var repository = Stub<ICustomerRepository>();

        // act
        repository.Stub(rep => rep.GetById(5)).Return(customer);

        // assert
        Assert.AreEqual(customer, repository.GetById(5));
    }

    [TestMethod]
    public void CanGetCustomerByDifId()
    {
        // arrange
        var customer = new Customer()
        {
            CustId = 5,
            DifId = "55",
            CustLookupName = "The Dude",
            LoginList = new[] {
                new Login { LoginCustId = 5, LoginName = "tdude" } }
        };

        var repository = Stub<ICustomerRepository>();

        // act
        repository.Stub(rep => rep.GetCustomerByDifID("55")).Return(customer);

        // assert
        Assert.AreEqual(customer, repository.GetCustomerByDifID("55"));
    }

    [TestMethod]
    public void CanGetCustomerByLogin()
    {
        // arrange
        var customer = new Customer()
        {
            CustId = 5,
            DifId = "55",
            CustLookupName = "The Dude",
            LoginList = new[] {
                new Login { LoginCustId = 5, LoginName = "tdude" } }
        };

        var repository = Stub<ICustomerRepository>();

        // act
        repository.Stub(rep =>
            rep.GetCustomerByLogin("tdude")).Return(customer);

        // assert
        Assert.AreEqual(customer, repository.GetCustomerByLogin("tdude"));
    }
}

Test Base Class

public class TestClassBase
{
    protected T Stub<T>() where T : class
    {
        return MockRepository.GenerateStub<T>();
    }
}

ICustomerRepository and IRepository

public interface ICustomerRepository : IRepository<Customer>
{
    IList<Customer> FindCustomers(string q);
    Customer GetCustomerByDifID(string difId);
    Customer GetCustomerByLogin(string loginName);
}

public interface IRepository<T>
{
    void Save(T entity);
    void Save(List<T> entity);
    bool Save(T entity, out string message);
    void Delete(T entity);
    T GetById(int id);
    ICollection<T> FindAll();
}