gistfile1.txt

public class SqlService {

	public string ConnectionStirng { get; private set; }

	public SqlService()
		:this("defaultConnectionString")
	{
	}

	public SqlService(stirng connectionString) {
		this.connectionString = connectionstring;
	}

	public virtual IList<User> GetUsers() {
		using(var cn = new SqlConnection("connectionString")) {
			const string sql = "select top 1o * from users where id=@userId";

			return cn.Query<User>(sql, new { userId = userId }).ToList();
		}
	}
}

public class SampleModule : NancyModule {
	
	public SampleModule(SqlService sql) {

		Get["/"] = _ => {

			var users = sql.GetUsers();
			return View["users", users];
		}

	}
}

public class FakeSqlService {
	public ovveride IList<User> GetUsers() {
		return new List<User>() {...};
	}

}