2 files changed, 28 insertions, 7 deletions
diff --git a/activerecord/test/cases/serialized_attribute_test.rb b/activerecord/test/cases/serialized_attribute_test.rb
index 673392b4c4..e1bdaab5cf 100644
--- a/activerecord/test/cases/serialized_attribute_test.rb
+++ b/activerecord/test/cases/serialized_attribute_test.rb
@@ -349,4 +349,32 @@ class SerializedAttributeTest < ActiveRecord::TestCase
     topic.foo
     refute topic.changed?
   end
+
+  def test_serialized_attribute_works_under_concurrent_initial_access
+    model = Topic.dup
+
+    topic = model.last
+    topic.update group: "1"
+
+    model.serialize :group, JSON
+    model.reset_column_information
+
+    # This isn't strictly necessary for the test, but a little bit of
+    # knowledge of internals allows us to make failures far more likely.
+    model.define_singleton_method(:define_attribute) do |*args|
+      Thread.pass
+      super(*args)
+    end
+
+    threads = 4.times.map do
+      Thread.new do
+        topic.reload.group
+      end
+    end
+
+    # All the threads should retrieve the value knowing it is JSON, and
+    # thus decode it. If this fails, some threads will instead see the
+    # raw string ("1"), or raise an exception.
+    assert_equal [1] * threads.size, threads.map(&:value)
+  end
 end
diff --git a/activerecord/test/cases/tasks/mysql_rake_test.rb b/activerecord/test/cases/tasks/mysql_rake_test.rb
index 33da3d11fc..c22d974536 100644
--- a/activerecord/test/cases/tasks/mysql_rake_test.rb
+++ b/activerecord/test/cases/tasks/mysql_rake_test.rb
@@ -294,13 +294,6 @@ if current_adapter?(:Mysql2Adapter)
         ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
       end
 
-      def test_structure_dump
-        filename = "awesome-file.sql"
-        Kernel.expects(:system).with("mysqldump", "--result-file", filename, "--no-data", "--routines", "--skip-comments", "test-db").returns(true)
-
-        ActiveRecord::Tasks::DatabaseTasks.structure_dump(@configuration, filename)
-      end
-
       def test_structure_dump_with_extra_flags
         filename = "awesome-file.sql"
         expected_command = ["mysqldump", "--result-file", filename, "--no-data", "--routines", "--skip-comments", "--noop", "test-db"]