RSpec query limit tests

gistfile1.txt

# From http://stackoverflow.com/a/13423584/153896
module ActiveRecord
  class QueryCounter
    attr_reader :query_count

    def initialize
      @query_count = 0
    end

    def to_proc
      lambda(&method(:callback))
    end

    def callback(_, _, _, _, values)
      @query_count += 1 unless %w(CACHE SCHEMA).include?(values[:name])
    end
  end
end

# Derived from http://stackoverflow.com/a/13423584/153896. Updated for RSpec 3.
RSpec::Matchers.define :exceed_query_limit do |expected|
  supports_block_expectations

  match do |block|
    query_count(&block) > expected
  end

  failure_message_when_negated do
    "Expected to run maximum #{expected} queries, got #{@counter.query_count}"
  end

  def query_count(&block)
    @counter = ActiveRecord::QueryCounter.new
    ActiveSupport::Notifications.subscribed(@counter.to_proc, 'sql.active_record', &block)
    @counter.query_count
  end
end

From Tim:
"for adding to spec helper
it allows you to create a spec dictating how many sql transaction you expect for a piece of code
I use it to add a expectation for few transactions
like when doing an .include.reference
where mutant wants to remove stuff because it is pure performance enhancement in AR
so I put a spect that runs the block and expects like 1 querey
where mutant would remove the .include
and end up with same result but multiple queries"