refactoring wallet amount to concern

app/models/concerns/amount_concern.rb

@@ -0,0 +1,23 @@
+module AmountConcern
+  extend ActiveSupport::Concern
+
+  included do
+    validates_numericality_of :amount, greater_than_or_equal_to: 0
+
+    def amount=(amount)
+      if amount.nil?
+        write_attribute(:amount, amount)
+      else
+        write_attribute(:amount, amount.to_i * 100)
+      end
+    end
+
+    def amount
+      if read_attribute(:amount).blank?
+        read_attribute(:amount)
+      else
+        read_attribute(:amount) / 100.0
+      end
+    end
+  end
+end

app/models/wallet.rb

@@ -1,16 +1,10 @@
 class Wallet < ActiveRecord::Base
+  include AmountConcern
+
   belongs_to :user
+  has_many :wallet_transactions, dependent: :destroy
 
   validates :user, presence: true
-  validates_numericality_of :amount, greater_than_or_equal_to: 0
-
-  def amount=(amount)
-    write_attribute(:amount, amount.to_i * 100)
-  end
-
-  def amount
-    read_attribute(:amount) / 100.0
-  end
 
   def credit(amount)
     if amount.is_a?(Numeric) and amount >= 0

app/models/wallet_transaction.rb

@@ -1,4 +1,6 @@
 class WalletTransaction < ActiveRecord::Base
+  include AmountConcern
+
   belongs_to :user
   belongs_to :wallet
   belongs_to :reservation

test/models/wallet_transaction_test.rb

@@ -2,7 +2,7 @@ require 'test_helper'
 
 class WalletTransactionTest < ActiveSupport::TestCase
   test 'transaction type must be credit or debit' do
-    transaction = WalletTransaction.new
+    transaction = WalletTransaction.new amount: 5
     transaction.transaction_type = 'credit'
     assert transaction.valid?
     transaction.transaction_type = 'debit'