seed.rb

## Create User

User.create! :first_name => "Test", :last_name => "User", :email => "test@dummy.com", :password => "password123"# add whatever other parameters you have here

# if you wanted to make user an admin (which I'm assuming you do if it's in a seed file) do:

u = User.create! :first_name => "Test", :last_name => "User", :email => "test@dummy.com", :password => "password123"

u.spree_roles << Spree::Role.find_or_create_by_name("admin")