Testing with_lock activerecord

with_lock_spec.rb

# For stackoverflow question: https://stackoverflow.com/questions/55339129/how-to-test-lock-mechanism

require "bundler/inline"

gemfile(true) do
  source "https://rubygems.org"

  git_source(:github) { |repo| "https://github.com/#{repo}.git" }

  # Activate the gem you are reporting the issue against.
  gem "activerecord", "5.2.0"
  gem "sqlite3", "~> 1.3.6"
  gem "rspec"
end

require "active_record"
require "logger"
require "rspec"

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: "sqlite3", database: ":memory:")
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :bank_accounts, force: true do |t|
  end

  create_table :transactions, force: true do |t|
  end

  create_table :bank_account_transactions, force: true do |t|
    t.integer :bank_account_id
    t.integer :bank_transaction_id
  end
end

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true
end

class BankAccount < ApplicationRecord; end
class Transaction < ApplicationRecord; end

class BankAccountTransaction < ApplicationRecord
  belongs_to :bank_account
  belongs_to :bank_transaction, class_name: "Transaction"
end

class ImportService
  def import_transactions(bank_account, transactions)
    bank_account.with_lock do
      transactions.each do |transaction|
        import(bank_account, transaction)
      end
    end
  end

  private

  def import(bank_account, transaction)
    BankAccountTransaction.create!(bank_account: bank_account,
                                   bank_transaction: transaction)
  end
end

RSpec.describe "BankAccount" do
  subject { BankAccount.new }
  let(:transactions) do
    # create 2 dummy transactions to pass to import method
    [Transaction.create!, Transaction.create!]
  end

  describe "#import_transactions" do
    it "runs with lock" do
      # Test if with_lock is getting called
      expect(subject).to receive(:with_lock) do |*_args, &block|
        # block is provided to with_lock method
        # execute the block and test if it creates transactions
        expect { block.call }
          .to change { BankAccountTransaction.count }.from(0).to(2)
      end

      ImportService.new.import_transactions(subject, transactions)
    end
  end
end