[guide] add article about ROMFactory

Author: Julien Amoros

source/4.0/guides/index.html.md

@@ -2,6 +2,7 @@
 title: Guides
 sections:
   - sql-quick-start
+  - testing
 ---
 
 Guides are a collection of short articles explaining how to achieve common tasks

source/4.0/guides/testing/factories.html.md

@@ -0,0 +1,140 @@
+---
+chapter: Testing
+title: Factories
+---
+
+When using ROM, you will need to test your code, and testing your code implies generating entities and use Factories to
+create records on your database. To do all of that, you can use `rom-factory`, which provides more or less same 
+functionnalities as `FactoryBot`.
+
+### Install RomFactory
+
+In your gemfile:
+
+```ruby
+gem 'rom-factory'
+```
+
+### Setup ROMFactory
+
+Then on your spec root file (like `spec_helper`), you have to initialize your factory:
+
+```ruby
+# Build database configuration
+db_config = { 
+  adapter: 'mysql2',
+  database: 'db_name',
+  host: 'database.host.io',
+  username: 'username',
+  password: 'password',
+  port: 3306
+}
+
+# Init your ROM container
+rom = ROM.container(:sql, db_config)do |config|
+        # Register ROM related files, especially Relations
+        config.auto_registration('../app/') # if your sources are in app folder
+      end
+
+# Declare your factory
+YourFactory = ROM::Factory.configure do |config|
+  config.rom = rom
+end
+
+# Load your factories' files
+Dir[App.root + '/spec/factories/**/*.rb'].each { |f| require f } # if you plan to put your factory files `spec/factories`
+```
+
+### Define your factory
+
+Then you can define your factories:
+
+```ruby
+YourFactory.define(:user) do |f|
+  f.sequence(:name) { |n| "User#{n}" }
+  f.website 'http://personal.website'
+  f.some_integer 42
+  f.created_at Time.now.utc
+end
+```
+
+You can define multiple builders on the same factory.
+In this example, the relation `users` (ie builder name pluralized) must exist in your ROM::RelationRegistry`.
+
+### Use your factory
+
+In your tests, you can either get an instance from your factory only in memory, or in memory but that has been 
+persisted on your database.
+
+Let's suppose that  `UserRepo` is your Users' repository and it has a relation to `users` SQL table. 
+
+```ruby
+user1 = YourFactory[:user]
+p user1
+#=> #<ROM::Struct::User id=84 name="User1" website="http://personnal.website" some_integer=42 created_at=2019-04-02 08:50:34 +0000>
+
+p UserRepo.users.by_pk(user1.id).one
+#=> #<ROM::Struct::User id=84 name="User1" website="http://personnal.website" some_integer=42 created_at=2019-04-02 08:50:34 +0000>
+
+user2 = YourFactory.structs[:user]
+p user2
+#=> #<ROM::Struct::User id=85 name="User2" website="http://personnal.website" some_integer=42 created_at=2019-04-02 08:50:46 +0000>
+
+p UserRepo.users.by_pk(user2.id).one
+#=> nil
+
+user3 = YourFactory.structs[:user, name: "toto", website: nil]
+p user3
+#=> #<ROM::Struct::User id=85 name="toto" website=nil some_integer=42 created_at=2019-04-02 08:51:20 +0000>
+```
+
+### Going further
+
+#### Associations
+
+RomFactory supports associations that you declared in your Relations.
+```ruby
+YourFactory.define(:user) do |f|
+  # this will use :team builder to create a team for a user
+  f.association(:team)
+
+  # this will create 2 posts for a user using :post builder
+  f.association(:posts, count: 2)
+end
+```
+
+#### Faker
+
+ROMFactory comes with Faker gem:
+
+```ruby
+YourFactory.define(:foo) do |f|
+  f.bar { fake(:number, :between, 10, 100) }
+end
+```
+
+#### Traits
+
+ROMFactory supports traits:
+
+```ruby
+YourFactory.define(:user) do |f|
+  f.registered true
+
+  f.trait :not_registered do |t|
+    t.registered false
+  end
+end
+
+p YourFactory[:user, :not_registered]
+#=> #<ROM::Struct::User id=130 registered=false>
+```
+
+### Inheritance
+You can extend existing builders, see [Rom Factory annoncement](https://rom-rb.org/blog/announcing-rom-factory/) for an
+example.
+
+
+### Read more:
+* [Rom Factory annoncement](https://rom-rb.org/blog/announcing-rom-factory/)
+* [Rom Factory repository](https://github.com/rom-rb/rom-factory/)

source/4.0/guides/testing/index.html.md

@@ -0,0 +1,7 @@
+---
+chapter: SQL How To
+sections:
+  - factories
+---
+
+In this section you can learn some tricks to test your code when using ROM.