add more testcases and doc about Hash#extract!

activesupport/CHANGELOG.md

@@ -1,12 +1,12 @@
 ## Rails 4.0.0 (unreleased) ##
 
-*   Hash#extract! returns only those keys that present in the reciever.
+*   Hash#extract! returns only those keys that present in the receiver.
 
         {:a => 1, :b => 2}.extract!(:a, :x) # => {:a => 1}
 
     *Mikhail Dieterle*
 
-*   Hash#extract! returns the same subclass, that the reciever is. I.e.
+*   Hash#extract! returns the same subclass, that the receiver is. I.e.
     HashWithIndifferentAccess#extract! returns HashWithIndifferentAccess instance.
 
     *Mikhail Dieterle*

activesupport/test/core_ext/hash_ext_test.rb

@@ -724,8 +724,10 @@ class HashExtTest < ActiveSupport::TestCase
   def test_extract
     original = {:a => 1, :b => 2, :c => 3, :d => 4}
     expected = {:a => 1, :b => 2}
+    remaining = {:c => 3, :d => 4}
 
     assert_equal expected, original.extract!(:a, :b, :x)
+    assert_equal remaining, original
   end
 
   def test_extract_nils
@@ -739,10 +741,15 @@ class HashExtTest < ActiveSupport::TestCase
   end
 
   def test_indifferent_extract
-    original = {:a => 1, :b => 2, :c => 3, :d => 4}.with_indifferent_access
+    original = {:a => 1, 'b' => 2, :c => 3, 'd' => 4}.with_indifferent_access
     expected = {:a => 1, :b => 2}.with_indifferent_access
+    remaining = {:c => 3, :d => 4}.with_indifferent_access
 
-    assert_equal expected, original.extract!(:a, :b)
+    [['a', 'b'], [:a, :b]].each do |keys|
+      copy = original.dup
+      assert_equal expected, copy.extract!(*keys)
+      assert_equal remaining, copy
+    end
   end
 
   def test_except

guides/source/active_support_core_extensions.md

@@ -2867,8 +2867,16 @@ The method `extract!` removes and returns the key/value pairs matching the given
 
 ```ruby
 hash = {:a => 1, :b => 2}
-rest = hash.extract!(:a) # => {:a => 1}
-hash                     # => {:b => 2}
+rest = hash.extract!(:a, :x) # => {:a => 1}     # non-existing keys are ignored
+hash                         # => {:b => 2}
+```
+
+The method `extract!` returns the same subclass of Hash, that the receiver is.
+
+```ruby
+hash = {:a => 1, :b => 2}.with_indifferent_access
+rest = hash.extract!(:a).class
+# => ActiveSupport::HashWithIndifferentAccess
 ```
 
 NOTE: Defined in `active_support/core_ext/hash/slice.rb`.