Our try

dave_kohei/convert_er.rb

@@ -0,0 +1,23 @@
+#coding:utf-8
+require 'date'
+
+class EraConverter
+  def self.convert(source_date)
+    parsed_date = DateTime.parse(source_date)
+    "#{self.era_from_date(parsed_date)}#{parsed_date.mon}月#{parsed_date.mday}日"
+  end
+
+  def self.era_from_date(source_date)
+    eras = [{ :start => Date.new(1989,1,8), :string => "平成" },
+            { :start => Date.new(1926,12,25), :string => "昭和" },
+            { :start => Date.new(1912,7,30), :string => "大正" },
+            { :start => Date.new(1868,9,8), :string => "明治" } ]
+
+    eras.each do |e|
+      if source_date >= e[:start]
+        year_string = source_date.year - (e[:start].year - 1)
+        return "#{e[:string]}#{year_string == 1 ? '元' : year_string}年"
+      end
+    end
+  end
+end

dave_kohei/test_era.rb

@@ -0,0 +1,25 @@
+#coding:utf-8
+
+require "minitest/autorun"
+require_relative "convert_er"
+require 'date'
+
+class TestEra < MiniTest::Unit::TestCase
+  def test_gets_era
+    #assert_equal "平成元年", EraConverter.era_from_date(Date.new(1989,1,8))
+    assert_equal "平成24年", EraConverter.era_from_date(Date.new(2012,1,8))
+    assert_equal "昭和54年", EraConverter.era_from_date(Date.new(1979,12,25))
+    assert_equal "大正2年", EraConverter.era_from_date(Date.new(1913,7,30))
+    assert_equal "明治11年", EraConverter.era_from_date(Date.new(1878,9,7))
+  end
+
+  def test_raise_on_unmat
+    assert_equal "平成24年10月20日",EraConverter.convert('2012-10-20')
+    assert_equal "昭和64年1月7日",EraConverter.convert('1989-1-7')
+    assert_equal "平成元年1月8日",EraConverter.convert('1989-1-8')
+    #assert_equal "昭和54年12月25日", EraConverter.era_from_date(Date.new(1979,12,25))
+    #assert_equal "大正2年", EraConverter.era_from_date(Date.new(1913,7,30))
+    #assert_equal "明治11年", EraConverter.era_from_date(Date.new(1878,9,7))
+
+  end
+end