1 files changed, 71 insertions, 0 deletions
diff --git a/activerecord/test/cases/migration/compatibility_test.rb b/activerecord/test/cases/migration/compatibility_test.rb
index 418793d1af..5753bd7117 100644
--- a/activerecord/test/cases/migration/compatibility_test.rb
+++ b/activerecord/test/cases/migration/compatibility_test.rb
@@ -137,6 +137,68 @@ module ActiveRecord
         assert connection.column_exists?(:testings, :updated_at, null: true)
       end
 
+      def test_timestamps_doesnt_set_precision_on_create_table
+        migration = Class.new(ActiveRecord::Migration[5.2]) {
+          def migrate(x)
+            create_table :more_testings do |t|
+              t.timestamps
+            end
+          end
+        }.new
+
+        ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+        assert connection.column_exists?(:more_testings, :created_at, null: false, **precision_implicit_default)
+        assert connection.column_exists?(:more_testings, :updated_at, null: false, **precision_implicit_default)
+      ensure
+        connection.drop_table :more_testings rescue nil
+      end
+
+      def test_timestamps_doesnt_set_precision_on_change_table
+        migration = Class.new(ActiveRecord::Migration[5.2]) {
+          def migrate(x)
+            change_table :testings do |t|
+              t.timestamps default: Time.now
+            end
+          end
+        }.new
+
+        ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+        assert connection.column_exists?(:testings, :created_at, null: false, **precision_implicit_default)
+        assert connection.column_exists?(:testings, :updated_at, null: false, **precision_implicit_default)
+      end
+
+      if ActiveRecord::Base.connection.supports_bulk_alter?
+        def test_timestamps_doesnt_set_precision_on_change_table_with_bulk
+          migration = Class.new(ActiveRecord::Migration[5.2]) {
+            def migrate(x)
+              change_table :testings, bulk: true do |t|
+                t.timestamps
+              end
+            end
+          }.new
+
+          ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+          assert connection.column_exists?(:testings, :created_at, null: false, **precision_implicit_default)
+          assert connection.column_exists?(:testings, :updated_at, null: false, **precision_implicit_default)
+        end
+      end
+
+      def test_timestamps_doesnt_set_precision_on_add_timestamps
+        migration = Class.new(ActiveRecord::Migration[5.2]) {
+          def migrate(x)
+            add_timestamps :testings, default: Time.now
+          end
+        }.new
+
+        ActiveRecord::Migrator.new(:up, [migration]).migrate
+
+        assert connection.column_exists?(:testings, :created_at, null: false, **precision_implicit_default)
+        assert connection.column_exists?(:testings, :updated_at, null: false, **precision_implicit_default)
+      end
+
       def test_legacy_migrations_raises_exception_when_inherited
         e = assert_raises(StandardError) do
           class_eval("class LegacyMigration < ActiveRecord::Migration; end")
@@ -176,6 +238,15 @@ module ActiveRecord
           ActiveRecord::Base.clear_cache!
         end
       end
+
+      private
+        def precision_implicit_default
+          if current_adapter?(:Mysql2Adapter)
+            { presicion: 0 }
+          else
+            { presicion: nil }
+          end
+        end
     end
   end
 end