Fix tests

activerecord/test/cases/migration/columns_test.rb

@@ -347,15 +347,17 @@ def test_change_column_null_with_non_boolean_arguments_raises
       end
 
       def test_change_column_null_does_not_change_default_functions
-        skip unless current_adapter?(:Mysql2Adapter, :TrilogyAdapter)
+        skip unless current_adapter?(:Mysql2Adapter, :TrilogyAdapter) && supports_default_expression?
 
-        connection.change_column_default "test_models", "created_at", -> { "(NOW())" }
+        function = connection.mariadb? ? "(current_timestamp())" : "(now())"
+
+        connection.change_column_default "test_models", "created_at", -> { function }
         TestModel.reset_column_information
-        assert_equal "(now())", TestModel.columns_hash["created_at"].default_function
+        assert_equal function, TestModel.columns_hash["created_at"].default_function
 
         connection.change_column_null "test_models", "created_at", true
         TestModel.reset_column_information
-        assert_equal "(now())", TestModel.columns_hash["created_at"].default_function
+        assert_equal function, TestModel.columns_hash["created_at"].default_function
       end
 
       def test_remove_column_no_second_parameter_raises_exception