A sample rspec spec to test concurrent api calls

a_sample_rspec_api_concurrent_call_spec.rb

require 'rails_helper'

describe Api::V1::CheckoutsController, type: :request do
  let(:user) do
    FactoryGirl.create(:user, current_balance: 100_000)
  end

  describe 'check concurrency' do
    it 'send multiple same requests', truncation_only: true do
      FactoryGirl.create(:item,
                         user: user,
                         amount: 10_000, item_uuid: '1234')
      FactoryGirl.create(:item,
                         user: user,
                         amount: 30_000, item_uuid: '5678')
      FactoryGirl.create(:item,
                         user: user,
                         amount: 20_000, item_uuid: 'abcd')

      headers = { 'ACCEPT' => 'application/json',
                  'HTTP_AUTHORIZATION' => http_basic_auth(user.api_key,
                                                          '') }
      threads = []
      threads << Thread.new do
        post '/api/v1/user/checkout',
             headers: headers,
             params: { item_uuids: %w[1234 5678] }
      end

      threads << Thread.new do
        post '/api/v1/user/checkout',
             headers: headers,
             params: { item_uuids: %w[1234 5678] }
      end

      threads << Thread.new do
        post '/api/v1/user/checkout',
             headers: headers,
             params: { item_uuids: %w[1234 5678] }
      end

      threads << Thread.new do
        post '/api/v1/user/checkout',
             headers: headers,
             params: { item_uuids: %w[1234 abcd] }
      end

      threads.each(&:join)
      user.reload
      expect(user.current_balance).to be >= 0
      expect(user.current_balance).to be 40_000
      expect(TransactionHistory.count).to eq 3
    end
  end
end

database_cleaner_strategies.rb

RSpec.configure do |config|
  config.use_transactional_fixtures = false

  config.before(:suite) do
    DatabaseCleaner.clean_with(:truncation)
  end

  config.before do |example|
    if example.metadata[:truncation_only]
      DatabaseCleaner.strategy = :truncation
      DatabaseCleaner.start
    else
      DatabaseCleaner.strategy = :transaction
      DatabaseCleaner.start
    end
  end

  config.after do
    DatabaseCleaner.clean
  end
end

Thank you @goromlagche 🙇‍♀️ I didn't used the config though but I killed the threads after the spec was done