Behaviour Driven Development - the whys and hows

@eldudi Behavior Driven Development Paweł Dudek

@eldudi What is a unit test? 2

@eldudi Kolawa, Adam; Huizinga, Dorota (2007). Automated Defect Prevention: Best
Practices in Software Management. “Unit testing is a method by which individual units of source code, sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures are tested to determine if they are ﬁt for use.” 3

@eldudi Um… what? 4

@eldudi “Unit testing is a method by which individual units
of source code, sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures are tested to determine if they are ﬁt for use.” 5 Kolawa, Adam; Huizinga, Dorota (2007). Automated Defect Prevention: Best Practices in Software Management.

@eldudi What is an app? 6

@eldudi An app is a set of behaviours created by
programmer and expected by user. 7

@eldudi We, programmers, have a limited cognition. As all humans
do. 8

@eldudi We can’t always ‘load’ all of the code of
our app into our memory. 9

@eldudi This means that we can, by accident, change the
behaviour of the app. 10

A B 12

A B 13

A B C 14

A B C 15

@eldudi Preserving behaviour of complex systems is hard. In fact,
of any system at all. 16

@eldudi Enter unit tests. 17

@eldudi Unit test is a failsafe to make sure app
behaviour is preserved. 18

@eldudi They are a proof that all components if your
app behave as expected 19

@eldudi Sounds like tests are a godsend, doesn’t it? 20

@eldudi What is a usual approach to testing? 21

@eldudi Random Project Manager “Lets just write tests afterwards.” 22

@eldudi No test harness 23

@eldudi Providing a proof whether program works after it has
been written increases burden on the programmer 24

@eldudi “Programmer should let the correctness proof and program grow
in hand.” –Edsger W. Dijkstra 25

@eldudi –Edsger W. Dijkstra “If one ﬁrst asks oneself what
the structure of a convincing proof would be and, having found this, then constructs a program satisfying this proof’s requirements, then these correctness concerns turn out to be a very effective heuristic guidance.” 26

@eldudi Write failing test 27

@eldudi Make it pass 28

@eldudi Red, Green 29

@eldudi Red, Green, Refactor 30

@eldudi TDD is born 31

@eldudi In TDD you always write test ﬁrst. Always. 32

@eldudi Which is then made green by writing/refactoring code 33

@eldudi TDD is not “just adding tests ﬁrst”. It’s a
complete workﬂow. 34

@eldudi TDD is a great way to determine how complex
your code has become. You just have to listen. 35

@eldudi Have to fake seven objects to isolate test? 36

@eldudi Have to inject a fake into a fake into
a fake? 37

@eldudi Your test setup method has 70 lines? 38

@eldudi This always points to an overcomplicated design And your
tests are here to point that out. Very clearly 39

@eldudi By writing test ﬁrst you’re becoming a consumer of
your upcoming API 40

Is that API hard to test? 41

That means it will probably be hard to consume too.
42

Or it will be really hard to maintain. 43

@eldudi But TDD didn’t really answer all the questions 44

@eldudi What should I test? 45

@eldudi How to explain what given test is testing? 46

@eldudi How to clarify requirements? 47

@eldudi How to provide examples? 48

@eldudi This is where BDD enters the stage 49

@eldudi BDD is quite simple 50

@eldudi But it requires a shift in how you perceive
your test suite 51

@eldudi When writing tests don’t think ‘tests’ 52

@eldudi Think about ‘behaviours’ 53

@eldudi Think about examples how your object should behave 54

@eldudi An objects behaviour is deﬁned by methods it declares
in its interface 55

@eldudi You should not be testing internal implementation of your
object 56

@eldudi BDD provides an ubiquitous language that helps understand what
are the requirements 57

@eldudi Example 58

@eldudi Tools 59

@eldudi Specta 60

@eldudi Expecta 61

@eldudi OCMockito 62

@eldudi Let’s do it! 63

What unit tests can’t do? 64

Unit tests are never a guarantee that you won’t ship
a bug. 65

But they’re damn good at greatly reducing amount of bugs.
And time spent on QA. 66

Are unit tests an invaluable tool for writing great software?
Heck yes. Am I going to produce a poor product if I can’t unit test? Hell no. Jonathan Rasmusson 67 http://agilewarrior.wordpress.com/2012/10/06/its-not-about-the-unit-tests/

@eldudi Thank you for your attention! 68

@eldudi Resources & Contact @eldudi github.com/paweldudek [email protected] Resources Contact objc.io/issue-15

Behaviour Driven Development - the whys and hows

Behaviour Driven Development - the whys and hows

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