forgeplus/spec/models/wallet_spec.rb

require 'rails_helper'

RSpec.describe Wallet, type: :model do
  describe 'receive' do
    it 'success' do
      wallet = Wallet.find_by_id(4)
      balance = wallet.balance
      amount = 5
      expect {
        wallet.receive(amount)
      }.to change { wallet.balance }.from(balance).to(balance+amount)
    end
  end

  describe 'pay' do
    context 'balance enough' do
      it 'success to pay' do
        wallet = Wallet.find_by_id(4)
        balance = wallet.balance
        amount = 5
        success = false
        expect {
          success = wallet.pay(amount)
        }.to change { wallet.balance }.from(balance).to(balance-amount)
        expect(success).to eq(true)
      end
    end

    context 'balance not enough' do
      it 'fail to pay' do
        wallet = Wallet.find_by_id(4)
        balance = wallet.balance
        amount = 500
        success = wallet.pay(amount)
        expect(success).to eq(false)
        expect(wallet.balance).to eq(balance)
      end
    end
  end
end