Behavior-Driven Development in Python @zacstewart 

import unittest 

import unittest import pyspec 

This Talk 

What is behavior-driven development? 

How does PySpec realize it? 

What's inside? 

Behavior-Driven Development 

Specific about behavior, not implementation 

G i v e n a n A T M A n d a d e b i t c a r d W h e n I w i t h d r a w $ 4 0 T h e n t h e A T M s h o u l d d i s p e n s e $ 4 0 

Ubiquitous language 

Stories and specifications 

PySpec 

Expectations 

# B o o l e a n a s s e r t i o n e x p e c t ( i s _ p r i m e ( 1 7 ) ) . t o ( b e ( T r u e ) ) # N e g a t i o n e x p e c t ( i s _ p r i m e ( 4 ) ) . n o t _ t o ( b e ( T r u e ) ) # E q u a l i t y e x p e c t ( f i z z b u z z ( 3 ) ) . t o ( e q ( ' f i z z ' ) ) 

# C o m p a r i s o n e x p e c t ( g o k u . p o w e r _ l e v e l ) . t o ( b e _ g t ( 9 0 0 0 ) ) # I n c l u s i o n e x p e c t ( l i b r a r y ) . t o ( i n c l u d e ( ' O n e H u n d r e d Y e a r s o f S o l i t u d e ' ) ) # R e g u l a r e x p r e s s i o n m a t c h i n g e x p e c t ( p a g e . b o d y ) . t o ( m a t c h ( r ' W e l c o m e , b a c k ! ' ) ) # E r r o r s e x p e c t ( c o n n e c t i o n . e x e c u t e , i n v a l i d _ q u e r y ) . t o ( r a i s e _ e r r o r ( I n v a l i d Q u e r y E r r o r ) ) 

Specifications 

w i t h s p e c i f i c a t i o n ( ' d i s p l a y s a w e l c o m e m e s s a g e ' ) : s i g n _ i n ( u s e r ) e x p e c t ( p a g e . b o d y ) . t o ( m a t c h ( r ' W e l c o m e , b a c k ! ' ) ) 

w i t h s p e c i f i c a t i o n ( ' d i s p e n s e s t h e m o n e y ' ) : a t m . w i t h d r a w ( 4 0 . 0 0 , c a r d = c a r d ) e x p e c t ( a t m . d i s p e n s a t i o n ) . t o ( e q ( 4 0 . 0 0 ) ) 

Contexts 

w i t h d e s c r i p t i o n ( A T M ) : a t m = A T M ( ) w i t h d e s c r i p t i o n ( ' . w i t h d r a w ' ) : c a r d = C a r d ( ) w i t h s p e c i f i c a t i o n ( ' d i s p e n s e s t h e m o n e y ' ) : a t m . w i t h d r a w ( 4 0 . 0 0 , c a r d = c a r d ) e x p e c t ( a t m . d i s p e n s a t i o n ) . t o ( e q ( 4 0 . 0 0 ) ) w i t h c o n t e x t ( ' w h e n u s e r h a s a c a r d f r o m a n o t h e r b a n k ' ) : c a r d = C a r d ( b a n k = ' O t h e r B a n k ' ) w i t h s p e c i f i c a t i o n ( ' n o t i f i e s t h e u s e r o f a f e e ' ) : a t m . w i t h d r a w ( 4 0 . 0 0 , c a r d = c a r d ) e x p e c t ( a t m . d i s p l a y ) . t o ( m a t c h ( r ' $ 3 . 0 0 f e e ' ) 

What's inside 

expect(actual).to(eq(expected)) e x p e c t creates a T a r g e t wrapping the a c t u a l value matcher functions like e q and i n c l u d e create M a t c h e r s with the e x p e c t e d value t o and n o t _ t o methods of T a r g e t verify that the M a t c h e r matches or does not match 

c l a s s E q u a l i t y M a t c h e r ( M a t c h e r ) : d e f m a t c h ( s e l f , e x p e c t e d , a c t u a l ) : r e t u r n e x p e c t e d = = a c t u a l @ p r o p e r t y d e f f a i l u r e _ m e s s a g e ( s e l f ) : r e t u r n " E x p e c t e d { 0 } t o b e e q u a l t o { 1 } " . f o r m a t ( s e l f . a c t u a l , s e l f . e x p e c t e d ) @ p r o p e r t y d e f f a i l u r e _ m e s s a g e _ w h e n _ n e g a t e d ( s e l f ) : r e t u r n " E x p e c t e d { 0 } n o t t o b e e q u a l t o { 1 } " . f o r m a t ( s e l f . a c t u a l , s e l f . e x p e c t e d ) d e f e q ( e x p e c t e d ) : r e t u r n E q u a l i t y M a t c h e r ( e x p e c t e d ) 

c l a s s P o s i t i v e H a n d l e r ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , a c t u a l , m a t c h e r ) : s e l f . a c t u a l = a c t u a l s e l f . m a t c h e r = m a t c h e r d e f r e s o l v e ( s e l f ) : i f n o t s e l f . m a t c h e r . m a t c h e s ( s e l f . a c t u a l ) : s e l f . h a n d l e _ f a i l u r e ( ) d e f h a n d l e _ f a i l u r e ( s e l f ) : r a i s e E x p e c t a t i o n N o t M e t E r r o r ( s e l f . m a t c h e r . f a i l u r e _ m e s s a g e ) 

with specification('dispenses the money'): 

c l a s s s p e c i f i c a t i o n ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , d e s c r i p t i o n ) : s e l f . d e s c r i p t i o n = d e s c r i p t i o n d e f _ _ e n t e r _ _ ( s e l f ) : p a s s d e f _ _ e x i t _ _ ( s e l f , t y p e , v a l u e , t r a c e b a c k ) : i f t y p e i s N o n e : s u i t e . r e p o r t _ s u c c e s s ( s e l f ) e l i f i s i n s t a n c e ( v a l u e , A s s e r t i o n E r r o r ) : s u i t e . r e p o r t _ f a i l u r e ( s e l f , v a l u e ) e l s e : s u i t e . r e p o r t _ e r r o r ( s e l f , v a l u e ) r e t u r n T r u e . . . 

with context('using a card from another bank'): 

c l a s s c o n t e x t ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , d e s c r i p t i o n = N o n e ) : s e l f . d e s c r i p t i o n = d e s c r i p t i o n d e f _ _ e n t e r _ _ ( s e l f ) : s u i t e . c o n t e x t = C o n t e x t ( s u i t e . c o n t e x t , s e l f . d e s c r i p t i o n ) d e f _ _ e x i t _ _ ( s e l f , t y p e , v a l u e , t r a c e b a c k ) : s u i t e . c o n t e x t = s u i t e . c o n t e x t . p a r e n t 

c l a s s S u i t e ( o b j e c t ) : d e f _ _ i n i t _ _ ( s e l f , o u t = s y s . s t d o u t ) : d e f i s _ g r e e n ( s e l f ) : d e f r e p o r t _ s u c c e s s ( s e l f , s p e c i f i c a t i o n ) : d e f r e p o r t _ f a i l u r e ( s e l f , s p e c i f i c a t i o n , f a i l u r e ) : d e f r e p o r t _ e r r o r ( s e l f , s p e c i f i c a t i o n , e r r o r ) : d e f r e p o r t _ r e s u l t s ( s e l f ) : 

The worst thing I've ever done to Python? 

d e f r u n _ s p e c ( f i l e n a m e ) : a s t = c o m p i l e ( o p e n ( f i l e n a m e , ' r b ' ) . r e a d ( ) , f i l e n a m e , ' e x e c ' ) e x e c ( a s t , g l o b a l s ( ) , l o c a l s ( ) ) 

Thank you! Questions? @zacstewart github.com/zacstewart/pyspec