Implementing the Self-Shunt testing pattern


#1

I just stumbled across the Self-Shunt unit testing pattern[0] and
decided, in my nuby quest to learn more about Ruby, to implement it in
Ruby. It’s simple enough thanks to duck-typing. Almost ridiculously so,
in fact.

My question, though, is: does the way I implemented this go against an
established ruby idiom or violate “the ruby way” in any way? If so I’d
love to hear it.

Thanks!
-dave

[0] http://www.objectmentor.com/resources/articles/SelfShunPtrn.pdf

===== self_shunt.rb
require ‘test/unit’

Implements self-shunt pattern in Ruby.

Self-shunt detailed at:

http://www.objectmentor.com/resources/articles/SelfShunPtrn.pdf

class Display
def display_item(item)
puts “The REAL display is showing: #item
# God only knows what other processing might take place here …
end
end

class Scanner

accepts any object having a #display_item(item) method

hooray duck typing :slight_smile:

def initialize(display)
@display = display
end
def scan(item)
@display.display_item(item)
end
end

completely pointless class to demonstrate the idea

class Item
def initialize(name)
@name = name
end
def to_s
@name
end
end

first test the self-shunt

class ScannerTest < Test::Unit::TestCase
def test_scan
scanner = Scanner.new(self)
item = Item.new(“test item”)
scanner.scan(item)
assert_equal(“test item”, @displayed_item.to_s)
end
def display_item(item)
@displayed_item = item
end
end

now do the real thing

def main # habits die hard… :slight_smile:
display = Display.new
scanner = Scanner.new(display)
scanner.scan Item.new(“now we are displaying the REAL item”)
2.times {puts} # to pad between this output and the test output
end

main


#2

DÅ?a Pondelok 13 Február 2006 06:16 Dave C. napísal:

-dave

[0] http://www.objectmentor.com/resources/articles/SelfShunPtrn.pdf

I -so- needed this PDF - self-shunt is the one thing that really
confused me
while skimming through Beck’s TDD:BE. Now if I can figure out how to do
this
in Java without getting a compiler induced headache, my job will be so
much
more fun…

main

Weakling :stuck_out_tongue_winking_eye: You forgot an if $0 == FILE, or however that idiom I
never use
anyway goes. Next thing we know, you’re hacking the interpreter to give
you
warnings about mismatched signedness of variables…

Anyways, thanks a lot for the code snippet, I have something to grok as
relaxation at last.

David V.


#3

I -so- needed this PDF - self-shunt is the one thing that really confused me
while skimming through Beck’s TDD:BE. Now if I can figure out how to do this
in Java without getting a compiler induced headache, my job will be so much
more fun…

Yeah, I remember seeing this pattern a while back somewhere else. Head
scratches and muttered “wtf” abounded. This made it ridiculously clear.

Anyways, thanks a lot for the code snippet, I have something to grok as
relaxation at last.

Sweet.