當我們希望對某個開發中的功能進行測試，
而那個功能需要其他物件的支援才能工作的話，
此時可以使用 double 來模擬
週邊物件並定義行為;
如此一來，
我們就能將精神完全投入在開發中的功能，
而不用同時兼顧其他地方。
假設我們現在想設計一個網站，
使用者在註冊時必須刷卡付費來使用內部服務。
倘若我們剛編寫了創造使用者的 create 方法，如下
users_controller.rb:
class UsersController < ApplicationController
... 程式碼省略 ...
def create
@user = User.new(user_params)
if @user.valid?
# 信用卡交易
charge = StripeWrapper::Charge.create(
:amount => 999, # in cents
:currency => "usd",
:card => params[:stripeToken],
:description => "Sign up for #{@user.email}"
)
if charge.successful?
@user.save
session[:user_id] = @user.id
AppMailer.delay.send_welcome_email(@user)
flash[:success] = "You are registered."
redirect_to home_path
else
flash[:danger] = charge.error_message
render :new
end
else
flash[:danger] = "There's something wrong during registration."
render :new
end
end
... 程式碼省略 ...
end
這個方法裡面，
使用了信用卡服務來索取註冊費用;
而當編寫測試時，
我們會希望單純地測試 create 方法的邏輯是否正確，
這時候就可以考慮使用 double 來模擬信用卡交易的行為
users_controller_spec.rb:
require "spec_helper"
describe UsersController do
describe "POST create" do
context "with valid personal info and valid card" do
# 當交易成功時 successful? 方法將回傳 true
let(:charge) { double(:charge, successful?: true ) }
before do
# 預期將會呼叫到 StripeWrapper::Charge.create 方法，並回傳 charge 物件
StripeWrapper::Charge.should_receive(:create).and_return(charge)
end
after { ActionMailer::Base.deliveries.clear }
it "creates the user" do
post :create, user: Fabricate.attributes_for(:user), stripeToken: "123"
expect(User.count).to eq 1
end
it "sets flash success message" do
post :create, user: Fabricate.attributes_for(:user), stripeToken: "123"
expect(flash[:success]).to be_present
end
it "redirects to the home page" do
post :create, user: Fabricate.attributes_for(:user), stripeToken: "123"
expect(response).to redirect_to home_path
end
it "sends out email to the user" do
post :create, user: { email: "alice@example.com", password: "password", full_name: "Alice Liddel" }
message = ActionMailer::Base.deliveries.last
expect(message.to).to eq ["alice@example.com"]
end
end
context "with valid personal info and declined card" do
# 交易失敗時，successful? 方法回傳 false， error_message 回傳錯誤訊息
let(:charge) { double(:charge, successful?: false, error_message: "Your card was declined." ) }
before do
# 預期將會呼叫到 StripeWrapper::Charge.create 方法，並回傳 charge 物件
StripeWrapper::Charge.should_receive(:create).and_return(charge)
end
after { ActionMailer::Base.deliveries.clear }
it "does not create the user" do
post :create, user: Fabricate.attributes_for(:user), stripeToken: "123"
expect(User.count).to eq 0
end
it "renders the :new template" do
post :create, user: Fabricate.attributes_for(:user), stripeToken: "123"
expect(response).to render_template :new
end
it "sets @user" do
post :create, user: Fabricate.attributes_for(:user), stripeToken: "123"
expect(assigns(:user)).to be_instance_of User
end
it "sets the flash danger message" do
post :create, user: Fabricate.attributes_for(:user), stripeToken: "123"
expect(flash[:danger]).to be_present
end
it "does not send out email" do
post :create, user: Fabricate.attributes_for(:user), stripeToken: "123"
expect(ActionMailer::Base.deliveries).to be_empty
end
end
context "with invalid personal info" do
after { ActionMailer::Base.deliveries.clear }
it "does not create the user" do
post :create, user: Fabricate.attributes_for(:user, password: "")
expect(User.count).to eq 0
end
it "renders the :new template" do
post :create, user: Fabricate.attributes_for(:user, password: "")
expect(response).to render_template :new
end
it "sets @user" do
post :create, user: Fabricate.attributes_for(:user, password: "")
expect(assigns(:user)).to be_instance_of User
end
it "sets the flash danger message" do
post :create, user: Fabricate.attributes_for(:user, password: "")
expect(flash[:danger]).to be_present
end
it "does not send out email" do
post :create, user: { email: "alice@example.com" }
expect(ActionMailer::Base.deliveries).to be_empty
end
end
end
end
在測試中模擬物件的技巧， 一方面讓我們可以專心地測試正在開發的功能， 另一方面，也可以縮短呼叫物件時等候回應的時間， 以提升測試效率。
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