該文章同步發佈於：我的部落格
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假如我遇到一段想重構的代碼，但不幸的是：
重構自己不理解的程式碼是有巨大的風險的，而且問題來了，如果我不知道他是做什麼的，那我要怎麼幫這段代碼寫測試呢？
有一個有趣的東西叫做：表徵測試，我是之前讀文章的時候看到的，他讓解決難題變得直接和簡單，等等會用一些簡單的範例做示範！
假設這是一段舊專案的程式碼。
下面的兩個方法 services_with_info & products_with_info 有幾個問題。一個是他們具有很大的重複性，還有這兩個方法其實並沒有真正的幫助，這兩個方法應該可以放到其他地方去，讓 Appointment 專注當一個 Appointment 的 Model，不必把 appointment_services & appointment_products 序列a化的過程放進來。
class Appointment < ActiveRecord::Base
def services_with_info
services.collect { |item|
item.serializable_hash.merge(
"price": number_with_precision(item.price, precision: 2),
"label": item.service.name,
"item_id": item.service.id,
"type": "service"
)
}
end
def products_with_info
products.collect { |item|
item.serializable_hash.merge(
"price": number_with_precision(item.price, precision: 2),
"label": item.product.name,
"item_id": item.product.id,
"type": "product"
)
}
end
end
這兩個方法中，我們先把目光放在 services_with_info，我的目標是抽離這個方法，創立一個抽象的概念，然後把主體移過去那邊。
重構時可能可以第一次就想到一個很棒的抽象概念，也可能不不行。我們可以先試試看一個抽象概念叫做 Appointment::ServiceCollection 的新類別。
下面是這個類別，目前做的就只是把 services_with_info 的內容複製貼上過來而已。
module Appointment
class ServiceCollection
def initialize(services)
@services = services
end
def to_h
@services.to_h { |item|
item.serializable_hash.merge(
"price": number_with_precision(item.price, precision: 2),
"label": item.service.name,
"item_id": item.service.id,
"type": "service"
)
}
end
end
end
當開始為這個新類別寫測試時，盡可能投入較少的經歷，先問自己一個問題，這個 ServiceCollection 能夠實體化物件嗎？
RSpec.describe Appointment::ServiceCollection do
describe '#to_h' do
it 'works' do
appointment_service = create(:appointment_service)
collection = Appointment::ServiceCollection.new([appointment_service])
end
end
end
剛剛的測試通過後，下一步將是期待一個看起來有點蠢的東西
RSpec.describe Appointment::ServiceCollection do
describe '#to_h' do
it 'works' do
appointment_service = create(:appointment_service)
collection = Appointment::ServiceCollection.new([appointment_service])
expect(collection.to_h).to eq('asdf')
end
end
end
我當然知道 collection.to_h 不會等於 'asdf'，但我不知道他等於什麼，所以任何的回傳值都會是錯誤。完全沒必要花心思去猜他會回傳什麼，反正測試結果會告訴我！
F
Failures:
1) Appointment::ServiceCollection#to_h works
Failure/Error: expect(collection.to_h).to eq('asdf')
TypeError:
wrong element type AppointmentService at 0 (expected array)
# ./app/models/appointment/service_collection.rb:7:in `to_h'
# ./app/models/appointment/service_collection.rb:7:in `to_h'
# ./spec/models/appointment/service_collection_spec.rb:8:in `block (3 levels) in <top (required)>'
Finished in 0.50943 seconds (files took 3.44 seconds to load)
1 example, 1 failure
因為是重構一個不知道會回傳什麼的方法，所以錯誤很正常，我們可以嘗試把程式碼註解掉。
module Appointment
class ServiceCollection
def initialize(services)
@services = services
end
def to_h
@services.to_h { |item|
#item.serializable_hash.merge(
#"price": number_with_precision(item.price, precision: 2),
#"label": item.service.name,
#"item_id": item.service.id,
#"type": "service"
#)
}
end
end
end
結果還是錯誤，那我們就註解掉更多的程式碼看看
module Appointment
class ServiceCollection
def initialize(services)
@services = services
end
def to_h
#@services.to_h { |item|
#item.serializable_hash.merge(
#"price": number_with_precision(item.price, precision: 2),
#"label": item.service.name,
#"item_id": item.service.id,
#"type": "service"
#)
#}
end
end
end
沒有太意外的還是錯誤，但結果改變了～
F
Failures:
1) Appointment::ServiceCollection#to_h works
Failure/Error: expect(collection.to_h).to eq('asdf')
expected: "asdf"
got: nil
(compared using ==)
# ./spec/models/appointment/service_collection_spec.rb:8:in `block (3 levels) in <top (required)>'
Finished in 0.49608 seconds (files took 3.41 seconds to load)
1 example, 1 failure
很明顯，問題出在 #@appointment_services.to_h { |item| 這行。問題大概是出在 to_h 身上，那我試著用 map 代替呢？
module Appointment
class ServiceCollection
def initialize(services)
@services = services
end
def to_h
@services.map { |item|
#item.serializable_hash.merge(
#"price": number_with_precision(item.price, precision: 2),
#"label": item.service.name,
#"item_id": item.service.id,
#"type": "service"
#)
}
end
end
end
成功了，這樣沒有得到像之前 wrong element type 的錯誤，而是不一樣的，更符合我們想看到的東西。
F
Failures:
1) Appointment::ServiceCollection#to_h works
Failure/Error: expect(collection.to_h).to eq('asdf')
expected: "asdf"
got: [nil]
(compared using ==)
Diff:
@@ -1,2 +1,2 @@
-"asdf"
+[nil]
# ./spec/models/appointment/service_collection_spec.rb:8:in `block (3 levels) in <top (required)>'
Finished in 0.48778 seconds (files took 3.5 seconds to load)
1 example, 1 failure
現在讓我把之前的註解都全部拔掉看看會怎麼樣～
module Appointment
class ServiceCollection
def initialize(services)
@services = services
end
def to_h
@services.map { |item|
item.serializable_hash.merge(
"price": number_with_precision(item.price, precision: 2),
"label": item.service.name,
"item_id": item.service.id,
"type": "service"
)
}
end
end
end
出現另一個不同的錯誤，說找不到 number_with_precision 這個方法
F
Failures:
1) Appointment::ServiceCollection#to_h works
Failure/Error: expect(collection.to_h).to eq('asdf')
NoMethodError:
undefined method `number_with_precision' for #<Appointment::ServiceCollection:0x007ff60274e640>
# ./app/models/appointment/service_collection.rb:9:in `block in to_h'
# ./app/models/appointment/service_collection.rb:7:in `map'
# ./app/models/appointment/service_collection.rb:7:in `to_h'
# ./spec/models/appointment/service_collection_spec.rb:8:in `block (3 levels) in <top (required)>'
Finished in 0.52793 seconds (files took 3.32 seconds to load)
1 example, 1 failure
剛好我們可以透過 Rails API 之後這個方法是放在哪裡，如果要在我們獨創的類別中使用，我們要 include ActionView::Helpers::NumberHelper 進來用。
module Appointment
class ServiceCollection
include ActionView::Helpers::NumberHelper
def initialize(services)
@services = services
end
def to_h
@services.map { |item|
item.serializable_hash.merge(
"price": number_with_precision(item.price, precision: 2),
"label": item.service.name,
"item_id": item.service.id,
"type": "service"
)
}
end
end
end
處理完這個問題後，我們終於可以看到回傳的結果是什麼了
F
Failures:
1) Appointment::ServiceCollection#to_h works
Failure/Error: expect(collection.to_h).to eq('asdf')
expected: "asdf"
got: [{"id"=>1, "appointment_id"=>1, "service_id"=>1, "created_at"=>Sun, 24 Feb 2019 16:45:16 EST -05:00, "updated_at"=>Sun, 24 Feb 2019 16:45:16 EST -05:00, "length"=>nil, "stylist_id"=>2, "price"=>"0.00", "label"=>"ve0xttqqfl", "item_id"=>1, "type"=>"service"}]
(compared using ==)
Diff:
@@ -1,2 +1,12 @@
-"asdf"
+[{"id"=>1,
+ "appointment_id"=>1,
+ "service_id"=>1,
+ "created_at"=>Sun, 24 Feb 2019 16:45:16 EST -05:00,
+ "updated_at"=>Sun, 24 Feb 2019 16:45:16 EST -05:00,
+ "length"=>nil,
+ "stylist_id"=>2,
+ "price"=>"0.00",
+ "label"=>"ve0xttqqfl",
+ "item_id"=>1,
+ "type"=>"service"}]
# ./spec/models/appointment/service_collection_spec.rb:8:in `block (3 levels) in <top (required)>'
Finished in 0.72959 seconds (files took 3.24 seconds to load)
1 example, 1 failure
看到回傳的結果真的很有趣，因為這是在重構一個舊專案，所以看到回傳值的時候就覺得好像要解開秘密了～
我們要用更現實的數值來進行測試。我知道測試會失敗，因為數值是隨意捏造的。
RSpec.describe Appointment::ServiceCollection do
describe '#to_h' do
it 'works' do
appointment_service = create(:appointment_service)
collection = Appointment::ServiceCollection.new([appointment_service])
item = collection.to_h.first
expect(item['price']).to eq('30.00')
expect(item['label']).to eq('Robert Chang')
expect(item['item_id']).to eq(appointment_service.item.id)
expect(item['type']).to eq('service')
end
end
end
這在執行測試是為了讓我的測試設置更符合我們期待的值！
RSpec.describe Appointment::ServiceCollection do
describe '#to_h' do
it 'works' do
appointment_service = create(
:appointment_service,
price: 30,
service: create(:service, name: 'Robert Change'))
collection = Appointment::ServiceCollection.new([appointment_service])
item = collection.to_h.first
expect(item['price']).to eq('30.00')
expect(item['label']).to eq('Robert Chang')
expect(item['item_id']).to eq(appointment_service.item.id)
expect(item['type']).to eq('service')
end
end
end
現在測試通過了，到目前為止，我們盡可能減少接觸原本程式碼的機會，因為我想最大限度的保留原本功能。現在我有了測試，我的測試可以保有原本的功能，而且我還可以自由地重構這段程式碼！
module Appointment
class ServiceCollection
include ActionView::Helpers::NumberHelper
ITEM_TYPE = 'service'
def initialize(services)
@services = services
end
def to_h
@services.map do |service|
service.serializable_hash.merge(extra_attributes(service))
end
end
private
def extra_attributes(service)
{
'price' => number_with_precision(service.price, precision: 2),
'label' => service.service.name,
'item_id' => service.service.id,
'type' => ITEM_TYPE
}
end
end
end
順便來整理一下測試的代碼：
RSpec.describe Appointment::ServiceCollection do
describe '#to_h' do
let(:appointment_service) do
create(
:appointment_service,
price: 30,
service: create(:service, name: 'Robert Chang')
)
end
let(:item) { Appointment::ServiceCollection.new([appointment_service]).to_h.first }
it 'adds the right attributes' do
expect(item['price']).to eq('30.00')
expect(item['label']).to eq('Robert Chang')
expect(item['item_id']).to eq(appointment_service.service.id)
expect(item['type']).to eq('service')
end
end
end
最後，我們就可以用我們新做的類別來取代原先的程式碼：
# 原本的
def services_with_info
services.collect { |item|
item.serializable_hash.merge(
"price": number_with_precision(item.price, precision: 2),
"label": item.service.name,
"item_id": item.service.id,
"type": "service"
)
}
end
# 現在的
def services_with_info
Appointment::ServiceCollection.new(services).to_h
end
這在重構的路上可以說是杯水車薪，但現在我們已經減少了很多的程式碼，因為其實 Rails 的 MVC 也沒有那麼夠用，並不是真的讓 Model 肥就是好，像這種取得資訊的方法，我們說不定可以把它全部拉出來整理！
但至少我們今天也知道了，如果一段程式碼他沒有測試，而且你還不知道他會回傳什麼的時候，嘗試看看這個表徵測試的方法，一步一步的找到能夠整理的邏輯，並且同時補上測試！
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