Add method for ensuring unique values (#752)

Add a method to Faker::Base that wraps the existing class and ensures
that the responses are unique.

README.md

@@ -11,7 +11,8 @@ development.
 
 ### NOTE
 
-* While Faker generates data at random, returned values are not guaranteed to be unique.
+* While Faker generates data at random, returned values are not guaranteed to be unique by default.
+  You must explicity specify when you require unique values, see [details](#ensuring-unique-values).
 * This is the `master` branch of Faker and may contain changes that are not yet released.
   Please refer the README of your version for the available methods.
   List of all versions is [available here](https://github.com/stympy/faker/releases).
@@ -79,6 +80,12 @@ Faker::Name.name      #=> "Christophe Bartell"
 Faker::Internet.email #=> "kirsten.greenholt@corkeryfisher.info"
 ```
 
+####Ensuring unique values
+Prefix your method call with `unique`. For example:
+```ruby
+Faker::Name.unique.name # This will return a unique name every time it is called
+```
+
 ### Faker::Address
 -----------------
 

lib/faker.rb

@@ -182,6 +182,10 @@ def rand_in_range(from, to)
         from, to = to, from if to < from
         Random.new.rand(from..to)
       end
+
+      def unique(max_retries = 10_000)
+        @unique_generator ||= UniqueGenerator.new(self, max_retries)
+      end
     end
   end
 end
@@ -239,3 +243,4 @@ def rand_in_range(from, to)
 require 'extensions/symbol'
 
 require 'helpers/char'
+require 'helpers/unique_generator'

lib/helpers/unique_generator.rb

@@ -0,0 +1,24 @@
+module Faker
+  class UniqueGenerator
+    def initialize(generator, max_retries)
+      @generator = generator
+      @max_retries = max_retries
+      @previous_results = Hash.new { |hash, key| hash[key] = Set.new }
+    end
+
+    def method_missing(name, *arguments)
+      @max_retries.times do
+        result = @generator.public_send(name, *arguments)
+
+        next if @previous_results[[name, arguments]].include?(result)
+
+        @previous_results[[name, arguments]] << result
+        return result
+      end
+
+      raise RetryLimitExceeded
+    end
+
+    RetryLimitExceeded = Class.new(StandardError)
+  end
+end

test/test_faker.rb

@@ -26,4 +26,12 @@ def test_regexify
     end
   end
 
+  def test_unique
+    unique_numbers = 8.times.map do
+      Faker::Base.unique.numerify('#')
+    end
+
+    assert_equal(unique_numbers.uniq, unique_numbers)
+  end
+
 end

test/test_faker_unique_generator.rb

@@ -0,0 +1,27 @@
+require File.expand_path(File.dirname(__FILE__) + '/test_helper.rb')
+
+class TestFakerUniqueGenerator < Test::Unit::TestCase
+
+  def test_generates_unique_values
+    generator = Faker::UniqueGenerator.new(Faker::Base, 10_000)
+
+    result = [generator.rand_in_range(1, 2), generator.rand_in_range(1, 2)]
+    assert_equal([1, 2], result.sort)
+  end
+
+  def test_returns_error_when_retries_exceeded
+    stubbed_generator = Object.new
+    def stubbed_generator.test
+      1
+    end
+
+    generator = Faker::UniqueGenerator.new(stubbed_generator, 3)
+
+    generator.test
+
+    assert_raises Faker::UniqueGenerator::RetryLimitExceeded do
+      generator.test
+    end
+  end
+
+end