diff --git a/pattern_generator.rb b/pattern_generator.rb
new file mode 100644
index 0000000..e1048cf
--- /dev/null
+++ b/pattern_generator.rb
@@ -0,0 +1,30 @@
+require 'pry'
+class PatternGenerator
+
+  def possible_serial_numbers(pattern)
+    pattern = pattern.chars
+    total = (pattern.count("N") * 10)*(pattern.count("X") * 26)
+    final = []
+    letters = [*('A'..'Z')]
+    numbers = [*(1..9)]
+    random_number = Random.rand(0..9)
+    random_letter = letters[Random.rand(0..26)]
+    until final.count == total
+      temp = []
+      pattern.each do |l|
+        if l == "N"
+          temp << random_number
+        elsif l == "X"
+          temp << random_letter
+        end
+        final = temp.join("")
+      end
+    end
+  end
+
+end
+
+# #
+# ##
+# ###
+# in JS
diff --git a/pattern_generator_test.rb b/pattern_generator_test.rb
new file mode 100644
index 0000000..c3f119d
--- /dev/null
+++ b/pattern_generator_test.rb
@@ -0,0 +1,39 @@
+gem 'minitest', '>= 5.0.0'
+require 'minitest/autorun'
+require 'minitest/pride'
+require_relative 'pattern_generator'
+
+class PatternGeneratorTest < Minitest::Test
+
+  def test_for_instance_of_class
+    skip
+    assert_instance_of PatternGenerator, PatternGenerator.new
+  end
+
+  def test_can_ouput_one_letter_serials
+    skip
+    p = PatternGenerator.new
+    assert_equal ["A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"], p.possible_serial_numbers("X")
+  end
+
+  def test_can_ouput_one_number_serials
+    skip
+    p = PatternGenerator.new
+    assert_equal ["1", "2", "3", "4", "5", "6", "7", "8", "9"], p.possible_serial_numbers("N")
+  end
+
+  def test_can_ouput_two_character_long_pattern
+    p = PatternGenerator.new
+    assert_includes ["AA", "AB"], p.possible_serial_numbers("XX")
+  end
+
+
+  def test_can_ouput_possible_serial_numbers
+    skip
+    p = PatternGenerator.new
+    assert_includes "AA1B2", p.possible_serial_numbers("XXNXN")
+  end
+
+
+
+end