Testing a rails model with a singleton in a validate method - ruby

Question

Very simple example:
Model:
require 'inventory'
class CustomerOrder < ActiveRecord::Base
validates_presence_of :name
validate :must_have_at_least_one_item, :items_must_exist
before_save :convert_to_internal_items
attr_accessor :items
after_initialize do
#convert the internal_items string into an array
if internal_items
self.items ||= self.internal_items.split(',').collect { |x| x.to_i }
else
# only clobber it if it hasn't been set yet, like in the constructor
self.items ||= []
end
end
private
def convert_to_internal_items
#TODO: convert the items array into a string
self.internal_items = self.items.join(',')
end
def must_have_at_least_one_item
self.items.size >= 1
end
def items_must_exist
self.items.all? do |item|
Inventory.item_exists?(item)
end
end
end
Inventory is a singleton that should provide access to another service out there.
class Inventory
def self.item_exists?(item_id)
# TODO: pretend real code exists here
# MORE CLARITY: this code should be replaced by the mock, because the actual
# inventory service cannot be reached during testing.
end
end
Right now the service does not exist, and so I need to mock out this method for my tests. I'm having trouble doing this the Right Way(tm). I'd like to have it be configurable somehow, so that I can put in the mock during my tests, but have the normal code run in the real world.
There's probably something I'm not wrapping my head around correctly.
EDIT: to be more clear: I need to mock the Inventory class within the validation method of the model. Eventually that will talk to a service that doesn't exist right now. So for my tests, I need to mock it up as if the service I were talking to really existed. Sorry for the confusion :(
Here's what I'd like to have in the specs:
describe CustomerOrder do
it "should not accept valid inventory items" do
#magical mocking that makes Inventory.item_exists? return what I want
magic.should_receive(:item_exists?).with(1).and_return(false)
magic.should_receive(:item_exists?).with(2).and_return(true)
co = CustomerOrder.new(:name => "foobar", :items => [1,2]
co.should_not be_valid
end
it "should be valid with valid inventory items" do
#magical mocking that makes Inventory.item_exists? return what I want
magic.should_receive(:item_exists?).with(3).and_return(true)
magic.should_receive(:item_exists?).with(4).and_return(true)
co = CustomerOrder.new(:name => "foobar", :items => [3,4]
co.should be_valid
end
end
Using rails 3.0.3, rspec 2 and cucumber. Of course, only the rspec part matters.

Answer 1

require 'spec_helper'
describe CustomerOrder do
it "is invalid without an existing Inventory item" do
item = mock('item')
customer = Customer.new(:name=>"Moe")
customer.stub(:items) { [item] }
Inventory.should_receive(:item_exists?).with(item).and_return(true)
customer.should_not be_valid
end
end
Note: untested.

Answer 2

The way I ended up solving this follows
Inventory class:
require 'singleton'
class Inventory
include Singleton
def self.set_mock(mock)
#mock = mock
end
def self.item_exists?(item_id)
return #mock.item_exists?(item_id) if #mock
# TODO: how should I stub this out for the api
end
end
CustomerOrder model:
require 'inventory'
class CustomerOrder < ActiveRecord::Base
validates_presence_of :name
validate :must_have_at_least_one_item, :items_must_exist
before_save :convert_to_internal_items
attr_accessor :items
after_initialize do
#convert the internal_items string into an array
if internal_items
self.items ||= self.internal_items.split(',').collect { |x| x.to_i }
else
# only clobber it if it hasn't been set yet, like in the constructor
self.items ||= []
end
end
private
def convert_to_internal_items
#TODO: convert the items array into a string
self.internal_items = self.items.join(',')
end
def must_have_at_least_one_item
errors.add(:items, "Must have at least one item") unless self.items.size >= 1
end
def items_must_exist
failed = self.items.find_all do |item|
!Inventory.item_exists?(item)
end
if !failed.empty? then
errors.add(:items, "Items with IDs: [#{failed.join(' ')}] are not valid")
end
end
end
CustomerOrder specs:
require 'spec_helper'
describe CustomerOrder do
fixtures :all
before do
fake = double('fake_inventory')
fake.stub(:item_exists?) do |val|
case val
when 1
true
when 2
true
when 3
false
end
end
Inventory.set_mock(fake)
#GRR, skipping my fixtures right now
#valid_order = CustomerOrder.new(:name => "valid order",
:items => [1,2])
end
it "should require a name and at least one item" do
co = CustomerOrder.new(:name => "valid", :items => [1])
co.should be_valid
end
it "should not be valid without any items" do
#valid_order.items = []
#valid_order.should_not be_valid
end
it "should not be valid without a name" do
#valid_order.name = nil
#valid_order.should_not be_valid
end
it "should expose items instead of internal_items" do
#valid_order.should respond_to(:items)
end
it "should be able to treat items like an array" do
#valid_order.items.size.should == 2
#valid_order.items.should respond_to(:<<)
#valid_order.items.should respond_to(:[])
end
it "should store items internally as a comma separated string" do
co = CustomerOrder.new(:name => "name", :items => [1,2])
co.save!
co.internal_items.should == "1,2"
end
it "should convert items to internal_items for saving" do
co = CustomerOrder.new(:name => "my order",
:items => [1,2])
co.name.should == "my order"
co.save!
co.internal_items.should == "1,2"
end
it "loads items from the database into the items array correctly" do
co = CustomerOrder.new(:name => "woot", :items => [2,1])
co.save.should == true
co2 = CustomerOrder.find_by_name("woot")
co2.items.should == [2,1]
end
it "is not valid with items that don't exist" do
#valid_order.items = [3,2,1]
#valid_order.should_not be_valid
end
it "ensures that items exist to be valid" do
#valid_order.items = [1,2]
#valid_order.should be_valid
end
end
This solution works, although it's probably not the best way to inject a mock into the Inventory Service at runtime. I'll try to do a better job of being more clear in the future.