This will fail for any month except the current month but will get the amount of Tuesdays in the current month.

TuesdaysCounter.rb

require 'minitest/autorun'
require 'date'
class TestWeekdayCounter < MiniTest::Unit::TestCase

	def test_number_of_tuesdays_in_june_2014_should_be_4
		thisMonth = Date.new(2014, 6, 1)
		nextMonth = Date.new(2014, thisMonth.month + 1, 1) - 1
		assert_equal 4, WeekdayCounter.new.get_tuesdays(thisMonth, nextMonth)
	end

 	def test_number_of_tuesdays_in_july_2014_should_be_5
		thisMonth = Date.new(2014, 7, 1)
		nextMonth = Date.new(2014, thisMonth.month + 1, 1) - 1
		assert_equal 5, WeekdayCounter.new.get_tuesdays(thisMonth, nextMonth)
  	end

end

class WeekdayCounter

	def get_tuesdays(start_date, end_date)
		tuesdays = 0
		(start_date..end_date).each do |date|
		  if date.wday.eql? 2 
		  	tuesdays = tuesdays + 1 
		  end
		end
		tuesdays
	end
	
end