This is a good implementation of that ying-yang pattern I was talking about, the only comment I'd make here is that for myself, I prefer to reference explicit values rather than using the return value of method calls in a test.  To illustrate what I mean, I'd have written this test like so:

```ruby
it "increases the field goal attempts by 1" do
  team.field_goals.attempts.should == 0; # Reference an explicit value...0
  team.make_field_goal
  team.field_goals.attempts.should == 1 # Again, using an explicit value
end
```