Simple example on how to count the number queries made by Active Record

instrument.rb

# Activate the gem you are reporting the issue against.
gem 'activerecord', '4.2.4'
require 'active_record'
require 'minitest/autorun'
require 'logger'

# Ensure backward compatibility with Minitest 4
Minitest::Test = MiniTest::Unit::TestCase unless defined?(Minitest::Test)

# 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 :posts do |t|
    t.timestamps null: false
  end
end

class Post < ActiveRecord::Base; end

class SQLCounter < ActiveSupport::Subscriber
  def sql(event)
    Thread.current[:query_count] ||= 0

    unless event.payload[:name] == 'SCHEMA'
      Thread.current[:query_count] += 1 unless event.payload[:sql] =~ /begin|commit|rollback/i
    end
  end
end

SQLCounter.attach_to :active_record

class InstrumentTest < Minitest::Test
  def setup
    @post = Post.create
    reset_query_count
  end

  def test_instrument_1
    assert_equal 0, query_count
  end

  def test_instrument_2
    @post.reload
    assert_equal 1, query_count
  end

  def test_instrument_3
    @post.touch
    assert_equal 1, query_count
  end

  def test_instrument_4
    @post.destroy
    assert_equal 1, query_count
  end

  def query_count
    Thread.current[:query_count]
  end

  def reset_query_count
    Thread.current[:query_count] = 0
  end
end