Created
May 17, 2012 17:13
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Global hard-coded dependencies are bad not only for design-related matters.
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class MyEvilDependency | |
def self.do_good | |
"ok" | |
end | |
def self.save_the_world | |
puts "I could destroy the world if I wanted" | |
end | |
end | |
class InjectedDependency | |
def do_good | |
"ok" | |
end | |
def save_the_world | |
puts "I would destroy the world but I can't" | |
end | |
end | |
class NaiveClass | |
def do_something | |
MyEvilDependency.do_good | |
MyEvilDependency.save_the_world | |
end | |
end | |
class AnotherClass | |
def initialize(other_obj) | |
@other_obj = other_obj | |
end | |
def do_something | |
@other_obj.do_good | |
@other_obj.save_the_world | |
end | |
end | |
describe NaiveClass do | |
describe "#my_other_method" do | |
it "trusts MyEvilDependency" do | |
MyEvilDependency.should_receive(:do_good) | |
NaiveClass.new.do_something | |
end | |
end | |
end | |
describe AnotherClass do | |
describe "#do_something" do | |
let(:obj) { double } | |
it "does what I want" do | |
obj.should_receive(:do_good) | |
AnotherClass.new(obj).do_something | |
end | |
end | |
end | |
# $ rspec global_dependency.rb | |
# I could destroy the world if I wanted | |
# .F | |
# | |
# Failures: | |
# | |
# 1) AnotherClass#do_something does what I want | |
# Failure/Error: @other_obj.save_the_world | |
# Double received unexpected message :save_the_world with (no args) | |
# # ./global_dependency.rb:35:in `do_something' | |
# # ./global_dependency.rb:56:in `block (3 levels) in <top (required)>' | |
# | |
# Finished in 0.00103 seconds | |
# 2 examples, 1 failure | |
# | |
# Failed examples: | |
# | |
# rspec ./global_dependency.rb:53 # AnotherClass#do_something does what I want |
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Basically, you have no control over the side effects of a global dependency.