Ruby module (rspec) to count and assert number of mongo queries

mongo_spy.rb

# Examples:
#
#   expect { code }.to change { finds("users") }.by(3)
#   expect { code }.to change { updates("contents") }.by(1)
#   expect { code }.not_to change { inserts }
#
#   MongoSpy.flush
#   ..code..
#   expect(MongoSpy.queries).to match(
#     "find" => { "users" => 1, "contents" => 1 },
#     "update" => { "users" => 1 }
#   )
#
# Reset numbers in a test or before(:each) (optional):
#
#   MongoSpy.flush
#
# View all numbers during a test:
#
#   pp MongoSpy.queries
#

module MongoSpy
  module Helpers
    %w(find delete insert update).each do |op|
      define_method(op.pluralize) { |ns = nil|
        ns ? MongoSpy.queries[op][ns] : MongoSpy.queries[op].values.sum
      }
    end
  end

  class << self
    def queries
      @queries ||= Hash.new { |h, k| h[k] = Hash.new(0) }
    end

    def flush
      @queries = nil
    end

    def started(event)
      op = event.command.keys.first # find, update, delete, createIndexes, etc.
      ns = event.command[op] # collection name
      return unless ns.is_a?(String)
      queries[op][ns] += 1
    end

    def succeeded(_); end
    def failed(_); end
  end
end

Mongo::Monitoring::Global.subscribe(Mongo::Monitoring::COMMAND, MongoSpy)

RSpec.configure do |config|
  config.include MongoSpy::Helpers
end