Use test range to generate NHS numbers (#2947)

The NHS sets aside a range of numbers for test purposes (999 000 0000 to
999 999 9999). Previously, this generator would generate valid NHS
numbers that may be in use by actual people in the UK health services.
This will now use the test range instead.

Author: neanias

doc/default/national_health_service.md

@@ -1,8 +1,9 @@
 # Faker::NationalHealthService
 
-```ruby
-Faker::NationalHealthService.british_number #=> "403 958 5577"
+The NHS sets aside a range of numbers from 999 000 0000 to 999 999 9999 for
+test purposes. For more details, see [NHS Digital documentation about
+synthetic data](https://digital.nhs.uk/services/e-referral-service/document-library/synthetic-data-in-live-environments#synthetic-data-naming-convention).
 
-# Keyword arguments: number
-Faker::NationalHealthService.check_digit(number: 400_012_114) #=> 6
+```ruby
+Faker::NationalHealthService.british_number #=> "999 464 0232"
 ```

lib/faker/default/national_health_service.rb

@@ -6,14 +6,17 @@ class << self
       ##
       # Produces a random British NHS number.
       #
+      # The NHS sets aside a range of numbers from 999 000 0000 to 999 999 9999
+      # for test purposes.
+      #
       # @return [String]
       #
       # @example
-      #   Faker::NationalHealthService.british_number #=> "403 958 5577"
+      #   Faker::NationalHealthService.british_number #=> "999 464 0232"
       #
       # @faker.version 1.9.2
       def british_number
-        base_number = rand(400_000_001...499_999_999)
+        base_number = rand(999_000_001...999_999_999)
         # If the check digit is equivalent to 10, the number is invalid.
         # See https://en.wikipedia.org/wiki/NHS_number
         base_number -= 1 if check_digit(number: base_number) == 10
@@ -24,6 +27,8 @@ def british_number
                                                            .join
       end
 
+      private
+
       ##
       # Produces a random British NHS number's check digit.
       #

test/faker/default/test_faker_national_health_service.rb

@@ -8,20 +8,12 @@ def setup
   end
 
   def test_nhs_british_number
-    assert_match(/\A\d{3}\s\d{3}\s\d{4}\z/, @tester.british_number)
+    assert_match(/\A9{3}\s\d{3}\s\d{4}\z/, @tester.british_number)
   end
 
   def test_check_digit_equals_10
-    Faker::NationalHealthService.stub(:rand, 458_617_434) do
-      assert_match('458 617 4331', @tester.british_number)
+    Faker::NationalHealthService.stub(:rand, 999_464_033) do
+      assert_match('999 464 0321', @tester.british_number)
     end
   end
-
-  def test_check_digit
-    assert_equal 6, @tester.check_digit(number: 400_012_114)
-  end
-
-  def test_check_digit_11
-    assert_equal 0, @tester.check_digit(number: 418_513_625)
-  end
 end