Add test cases for german phone numbers
user
```ruby
# encoding: utf-8

# => author: lawitschka
# => email: moritz.lawitschka@urbanvention.com
require 'helper'

class TestPhoneNumberDE < Test::Unit::TestCase
  def setup
    @tester = Faker::PhoneNumberDE
  end

  def test_mobile_prefix
    assert_match /^01[567]{1}[0-9]{1}$/, Faker::PhoneNumberDE.mobile_prefix
  end

  def test_mobile_prefix_without_leading_zero
    assert_match /^1[567]{1}[0-9]{1}$/, Faker::PhoneNumberDE.mobile_prefix(false)
  end

  def test_region_prefix
    assert_match /^0[2-9]{1}[0-9]{1,3}$/, Faker::PhoneNumberDE.region_prefix
  end

  def test_region_prefix_without_leading_zero
    assert_match /^[2-9]{1}[0-9]{1,3}$/, Faker::PhoneNumberDE.region_prefix(false)
  end

  def test_mobile_phone_number
    assert_match /^01[567]{1}[0-9]{1} [0-9]{7}$/, Faker::PhoneNumberDE.mobile_phone_number
  end

  def test_home_work_phone_number
    assert_match /^0[2-9]{1}[0-9]{1,3} [0-9]{7}$/, Faker::PhoneNumberDE.home_work_phone_number
  end

  def test_country_code
    assert_match '+49', Faker::PhoneNumberDE.country_code
  end

  def test_international_mobile_phone_number
    assert_match /^\+49 1[567]{1}[0-9]{1} [0-9]{7}$/, Faker::PhoneNumberDE.international_mobile_phone_number
  end

  def test_international_home_work_phone_number
    assert_match /^\+49 [2-9]{1}[0-9]{1,3} [0-9]{7}$/, Faker::PhoneNumberDE.international_home_work_phone_number
  end

end```
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