gistfile1.cs

// re: for http://codemanship.co.uk/parlezuml/blog/?postid=1149

// original code, called from inside the method:
Customer customer = DataRepository.GetCustomer(customerId);

// to enable the creation of the regression suite, 
// I extract the implementation of DataRepository.GetCustomer into its own methpd

class DataRepository {
    public static Customer GetCustomer(customerId) {
        return DataRepository.getCustomer(customerId);
    }

    private static Customer getCustomer(customerId) {
        return ...
    }
}

// now I change the public static method into a Func<Customer, int> property and
// initialize it to the private method


class DataRepository {
    public static Func<Customer, int> GetCustomer = DataRepository.getCustomer;

    private static Customer GetCustomer(customerId) {
        return ...
    }
}

// now I can write the tests using this "StubRepository" implementation
public class StubRepository
    {
        private readonly Customer customer;

        public StubRepository(Customer customer)
        {
            this.customer = customer;
            DataRepository.getCustomer = customerId => customer;
        }
}

// once I have the desired regression suite, I just refactor the internals properly to a similar
// implemnetation to Jason Gorman's