Support hash as first argument in `assert_difference`. (#31600)

* Support hash as first argument for `assert_difference`.

This allows to specify multiple numeric differences in the same assertion.
Example:

    assert_difference 'Article.count' => 1, 'Notification.count' => 2 do
      # post :create, params: { article: {...} }
    end

* Support error message when passing a hash as a first parameter

* Format CHANGELOG properly

[Julien Meichelbeck + Rafael Mendonça França]

1 files changed, 7 insertions, 0 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index a21a817fbb..acff6367f2 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,3 +1,10 @@
+*   Support hash as first argument in `assert_difference`. This allows to specify multiple
+    numeric differences in the same assertion.
+
+        assert_difference ->{ Article.count } => 1, ->{ Post.count } => 2
+
+    *Julien Meichelbeck*
+
 *   Add missing instrumentation for `read_multi` in `ActiveSupport::Cache::Store`.
 
     *Ignatius Reza Lesmana*