Fairly recently we investigated a runtime error while running cron jobs against our subscription purchases. The error stemmed from a class mismatch when a method method_foo was returning a SubscriptionFoo object when we were expecting a SubscriptionBar object. The solution was fairly straight forward, however writing a well-scoped test for method_foo and its return value was not. Why? Because it is often overlooked to write well-scoped tests for relatively large applications in favor of writing narrow-scoped tests that strictly test what you want. Tests should be just as scalable, flexible and maintainable as our main code.
The initial attempt was to test method_foo's class return types: SubscriptionFoo or SubscriptionBar.
The code was relatively simple:
describe FooBar do
describe '#method_foo' do
context 'when it should return a SubscriptionTypeFoo' do
...