From 564b162015bebe4d393ee1160f081aae8c4da1d7 Mon Sep 17 00:00:00 2001
From: Lucas Mazza <lucastmazza@gmail.com>
Date: Thu, 24 Sep 2015 13:32:08 -0300
Subject: [PATCH] Make `assert_difference` return the result of the yielded
 block.

With this we can perform new assertions on the returned value without having
to cache it with an outer variable or wrapping all subsequent assertions inside
the `assert_difference` block.

Before:

```
post = nil
assert_difference -> { Post.count }, 1 do
  Post.create
end

assert_predicate post, :persisted?
```

Now:

```
post = assert_difference -> { Post.count } do
  Post.create
end

assert_predicate post, :persisted?
```
---
 activesupport/CHANGELOG.md                          | 13 ++++++++++++-
 .../lib/active_support/testing/assertions.rb        |  4 +++-
 activesupport/test/test_case_test.rb                |  8 ++++++++
 3 files changed, 23 insertions(+), 2 deletions(-)

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 309d842da1..a39344e464 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,14 @@
+*   `assert_difference` and `assert_no_difference` now returns the result of the
+    yielded block.
+
+    Example:
+
+      post = assert_difference -> { Post.count }, 1 do
+        Post.create
+      end
+
+    *Lucas Mazza*
+
 *   Short-circuit `blank?` on date and time values since they are never blank.
 
     Fixes #21657
@@ -12,7 +23,7 @@
 *   Updated Unicode version to 8.0.0
 
     *Anshul Sharma*
-    
+
 *   `number_to_currency` and `number_with_delimiter` now accept custom `delimiter_pattern` option
      to handle placement of delimiter, to support currency formats like INR
 
diff --git a/activesupport/lib/active_support/testing/assertions.rb b/activesupport/lib/active_support/testing/assertions.rb
index d87ce3474d..ae8c15d8bf 100644
--- a/activesupport/lib/active_support/testing/assertions.rb
+++ b/activesupport/lib/active_support/testing/assertions.rb
@@ -68,13 +68,15 @@ def assert_difference(expression, difference = 1, message = nil, &block)
         }
         before = exps.map(&:call)
 
-        yield
+        retval = yield
 
         expressions.zip(exps).each_with_index do |(code, e), i|
           error  = "#{code.inspect} didn't change by #{difference}"
           error  = "#{message}.\n#{error}" if message
           assert_equal(before[i] + difference, e.call, error)
         end
+
+        retval
       end
 
       # Assertion that the numeric result of evaluating an expression is not
diff --git a/activesupport/test/test_case_test.rb b/activesupport/test/test_case_test.rb
index 9e6d1a91d0..18228a2ac5 100644
--- a/activesupport/test/test_case_test.rb
+++ b/activesupport/test/test_case_test.rb
@@ -56,6 +56,14 @@ def test_assert_difference
     end
   end
 
+  def test_assert_difference_retval
+    incremented = assert_difference '@object.num', +1 do
+      @object.increment
+    end
+
+    assert_equal incremented, 1
+  end
+
   def test_assert_difference_with_implicit_difference
     assert_difference '@object.num' do
       @object.increment