TDD Outside-In
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Commented slides for my WebExpo and JUG Ostrava talk. See full recording here: http://vimeo.com/51208668
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TDD Outside-In
- 1. TDD OUTSIDE-‐IN Daniel Kolman @kolman blog.kolman.cz www.vendavo.cz
- 2. UNIT TESTS ARE NOT ABOUT FINDING BUGS …so what they are about? hCp://www.flickr.com/photos/rupert_brun/6658715247
- 3. BOTTOM-‐UP vs. OUTSIDE-‐IN There are two styles of wriXng programs
- 4. BOTTOM-‐UP You can write program starXng with the low-‐level code
- 5. BOTTOM-‐UP E.g. you start with database and data access code and conXnue up to the UI UI Controllers Domain Model Data Access DB Schema
- 6. OUTSIDE-‐IN Or you can start with UI or some business logic, postponing the low-‐level details unXl really necessary…
- 7. OUTSIDE-‐IN …because the low-‐ level details have no business value hCp://indeb^atshortbadteeth.wordpress.com/2012/01/20/hello-‐goals-‐for-‐a-‐fortnight-‐thursday-‐results-‐for-‐challenge-‐1-‐and-‐new-‐goal/
- 8. OUTSIDE-‐IN When wriXng program outside-‐in, you need to replace the low-‐level code with mocks – it was not wriCen yet See the video recording for demo how to do it
- 9. So we have seen in demo how to write program from tests and we may now understand that… UNIT TESTS ARE NOT (just) ABOUT FINDING BUGS …but why? And what they are about? hCp://www.flickr.com/photos/rupert_brun/6658715247
- 10. EXTERNAL QUALITY vs. INTERNAL QUALITY First, we need to have a look at two kinds of quality in computer sofware
- 11. EXTERNAL QUALITY how well the system meets the needs of its customers and users (is it funcXonal, reliable, available, responsive...) hCp://www.youtube.com/watch?v=SLikJ1c53wc
- 12. INTERNAL QUALITY how well it meets the needs of its developers and administrators (is it easy to understand, easy to change...)
- 13. UNIT TEST Test Unit test execute the object in isolaXon, mocking all dependencies… …but what can this test tell us about external quality?
- 14. Of course nothing! USER Because users execute the applicaXon like this: User And this is how end-‐ to-‐end test works.
- 15. There is a great book on this topic…
- 16. …and it contains this charts, explaining what kind of feedback is provided by different kinds of Unit test tells us a lot tests about the internal quality of the code… …while end-‐to-‐end test provides a lot of feedback about the external quality of the app
- 17. Which means that… UNIT TESTS ARE NOT ABOUT FINDING BUGS …because… hCp://www.flickr.com/photos/rupert_brun/6658715247
- 18. UNIT TESTS ARE DESIGN TOOL …that helps keeping the code clean and maintainable hCp://www.flickr.com/photos/shelfappeal/4531230129
- 19. EASY TO TEST = WELL DESIGNED
- 20. HARD TO TEST = BADLY DESIGNED …because the unit tests tell us a lot about internal quality of the code
- 21. Therefore, if you want to write unit tests… FIX CODE FIRST! Otherwise you will spend ages wriXng terrible, ugly and long unit tests, just to find out that the internal quality of the code is bad
- 22. It makes no sense to unit test this: …without trying to improve the internal design hCp://www.flickr.com/photos/daveparker/28335459
- 23. Odkazy k přednášce najdete na hCp://blog.kolman.cz Because… UNIT TESTS ARE DESIGN TOOL Thank you! Daniel Kolman @kolman blog.kolman.cz www.vendavo.cz