Test Doubles
Unleash the Doppelgängers
Franck Arrecot & Kevin Ottens
Akademy 2015
UPS ~ Zanshin ~ KDAB
KDE ~ PhD ~ UPS ~ KDAB
TDD !!!
Test Doubles
In automated unit testing, it may be necessary to use objects or procedures that look and behave like their release-intended counterparts, but are actually simplified versions that reduce the complexity and facilitate testing.
(Wikipedia)
Doppelgängers?
In fiction and folklore, a doppelgänger is a look-alike or double of a living person, sometimes portrayed as a paranormal phenomenon […]
(Wikipedia)
Dummies
Dummies are used when a parameter is needed for the tested method but without actually needing to use the parameter
Kevin? You’re boring…
Franck? Please show some code!
- ✔ Can be as simple as `nullptr`
- ✔ Reduce the amount of collaborators in tests
- ✘ Not enforcing anything
- ✘ Code under test has to cope with dummies
Stubs
Stubs are used for providing the tested code with indirect input
Kevin? Still here? really??
Franck? The stage is your!
- ✔ Fosters simple readable tests
- ✔ Can be done with mocking frameworks
- ✘ No clue on how results are obtained
- ✘ Might push to write extra classes
Mocks
Mocks are used for verifying indirect output of the tested code
Kevin? *yawn*
Go Franck! Go!
- ✔ Better test isolation
- ✔ Verify protocols between objects
- ✘ More verbose test code
- ✘ Makes refactoring harder
Fakes
Fakes are used as a simpler implementation of a system (e.g. in-memory database)
Kevin? Please… make it stop…
Franck? Impress us with a last example!
- ✔ Simplifies test code
- ✔ Potential test speed up
- ✘ Lots of extra code to maintain
- ✘ Generally has its own test suite