Here we indicate (using the time helpers discussed in Box 8.1) that the second post was created more recently, i.e., 1.hour.ago, while the first post was created 1.day.ago. Note how convenient the use of Factory Girl is: Not only can we assign the user using mass assignment (since factories bypass attr_accessible), we can also set created_ at manually, which Active Record won’t allow us to do. (Recall that created_at and updated_at are ‘‘magic’’ columns, automatically set to the proper creation and update timestamps, so any explicit initialization values are overwritten by the magic.)

     Most database adapters (including the one for SQLite) return the microposts in order of their ids, so we can arrange for an initial test that almost certainly fails using the code in Listing 10.13. This uses the let! (read ‘‘let bang’’) method in place of let; the reason is that let variables are lazy, meaning that they only spring into existence when referenced. The problem is that we want the microposts to exist immediately, so that the timestamps are in the right order and so that @user.microposts isn’t empty. We accomplish this with let!, which forces the corresponding variable to come into existence.