使 用 Mock object
进 行 测 试
张 元 一

什么是Mock object？

wikipedia
Mock object 是面向对象编程中
，对真实对象的行为以可控的
方式进行模拟的一种虚拟对象

汽车碰撞测试中的模型人

为什么需要Mock object？

1.降低代码耦合

一个改动导致大量测试失败

def test_create
post :create, :user =>
{:name => 'test'}
end
def test_update
put :update, :user =>
{:name => 'new'}
end

add_column :first_name
add_column :last_name
remove_column :name
挂了！

2. 人生短暂,珍惜时间

不要重复测试
A测试例中已经测试过的代
码没必要再在B测试例中进
行测试,尤其是这些代码很耗
时

# post_test.rb
def test_should_create_post
post = Post.new(...)
assert post.valid?
end
class post
validates_presence_of :xxx
end

# posts_controller_test.rb
def test_should_create_post
post :create,
:post => {...}
...
end

# posts_controller.rb
def create
post = Post.new(params[:post])
if post.save
...
end
重复了！

3.让自己更轻松

等待是人世间最痛苦的事情之一,
尤其是你苦苦等待的结果居然是：
Failure!

如何使用Mock object？

Mocha, Flex Mock or RSpec

Mocha

@post = mock(“post”)
@post = Post.new

@post = mock(“post”)
@post.digg
#<Mock:post>.digg -
expected calls: 0, actual
calls: 1

@post.expects(:digg)
@post.instance_eval {
def digg
...
end
}

def test_xxx
@post.expects(:digg)
end
#<Mock:post>.digg -
expected calls: 1, actual
calls: 0

@post.expects(:digg).once
at_least(min)
at_least_once
at_most(max)
at_most_once
never
times(num)

if @post.digg # nil
...
else
...
end

@post.expects(:digg)
.returns(true)
@post.expects(:digg)
.raises(exception)

@post.digg(@blocked) # false
@post.digg(@unblocked) # true
@post.expects(:digg)
.with(any_of(User.blocked))
.returns(false)
@post.expects(:digg)
.with(any_of(User.unblocked))
.returns(true)

all_of
any_of
anything
has_entry(key, value)
has_key(key)
has_value(value)
includes(item)
instance_of(klass)
kind_of(klass)
regexp_matches(regexp)

@post.expects(:method)
.at_least(0)
@post.expects(:method)
.at_least(0)
.returns(:result)
@post.stubs(:method)
@post.stubs(:method =>
:result)

@post = stub_everything('post'
:method => :result)
@post.method1 # nil
@post.method2 # nil
@post.method # :result

Mocha on Rails

def test_create
post :create, :user =>
{:name => 'test'}
end
add_column :first_name
add_column :last_name
remove_column :name

def test_should_create_user
Post.expects(:new)
.returns(@post)
@post.expects(:save)
.returns(true)
post :create, :user => {}
assert_redirect_to
user_path(@user)
end

告别Fixture！

# teachers_students.yml
one:
teacher_id: 1
不够直观 student_id: 1
two:
teacher_id: 1
浪费时间 student_id: 2
three:
teacher_id: 2
student_id: 3

def setup
@user = User.new(:name=>'test')
@post1 =
Post.new(:title=>'post1')
end
def test_should_show_post
User.expects(:find)
.returns(@user)
@user.posts.expects(:find)
.returns(@post1)
get :show, :id=>1, :user_id=>1
assert_response :success
end

RSpec

it “should create a new user” do
User.should_receive(:new)
.and_return(@user)
User.stub!(:save)
.and_return(true)
post :create, :user => {}
response.should
redirect_to(user_path(@user))
end

Flex Mock?
同样的思想,不同的实现！

问题?

谢谢!