Ruby: Writing specs for (partially) memoized code
When you're writing specs for ActiveRecord models that use memoization, a simple
#reload will not do:
it 'updates on changes' do subject.seat_counts =  subject.seat_total.should == 5 # seat_total is either memoized itself, or using some # private memoized method subject.seat_counts = [5, 1] subject.seat_total.reload.should == 6 # => Still 5 end
You might be tempted to manually unmemoize any memoized internal method to get
#seat_total to update, but that has two disadvantages:
1) You're doing something that never happens in reality. Your tests shouldn't do things your code never does.
2) You're fiddling with internal state. When writing tests, stay on your chosen abstraction level.
Perform a full reload by re-finding your record:
it 'updates on changes' do subject.seat_counts =  subject.seat_total.should == 5 subject.seat_counts = [5, 1] # Re-find subject to wipe memoization subject = described_class.find(subject.id) subject.seat_total.reload.should == 6 # Passes end
Note that this does not work if you're testing unpersisted new records. In this case, there's probably something conceptually wrong and you either shouldn't expect to see updates or shouldn't memoize at all.