test: add rotation system config test case

Signed-off-by: Kentaro Hayashi <hayashi@clear-code.com>

test/config/test_system_config.rb

@@ -143,5 +143,23 @@ def parse_text(text)
       sc.overwrite_variables(**s.for_system_config)
       assert_equal(level, sc.log_level)
     end
+
+    sub_test_case "log rotation" do
+      test "rotate without age" do
+        conf = parse_text(<<-EOS)
+          <system>
+            <log>
+              rotate_age 3
+              rotate_size 300
+            </log>
+          </system>
+      EOS
+        s = FakeSupervisor.new
+        sc = Fluent::SystemConfig.new(conf)
+        sc.overwrite_variables(**s.for_system_config)
+        assert_equal("3", sc.log.rotate_age)
+        assert_equal(300, sc.log.rotate_size)
+      end
+    end
   end
 end

test/test_supervisor.rb

@@ -489,6 +489,35 @@ def test_logger_with_rotate_age_and_rotate_size(rotate_age)
     assert_equal 10, $log.out.instance_variable_get(:@shift_size)
   end
 
+  sub_test_case "system log rotation" do
+    def test_default_log_rotate_age
+      require "tempfile"
+      Tempfile.open do |file|
+        config =<<-EOS
+<system>
+  <log>
+    rotate_age: 3
+    rotate_size: 300
+  </log>
+</system>
+EOS
+        file.puts(config)
+        file.flush
+        opts = Fluent::Supervisor.default_options.merge(
+          log_path: "#{TMP_DIR}/test.log", config_path: file.path
+        )
+        sv = Fluent::Supervisor.new(opts)
+
+        log = sv.instance_variable_get(:@log)
+        log.init(:standalone, 0)
+        logger = $log.instance_variable_get(:@logger)
+
+        assert_equal(3, logger.instance_variable_get(:@rotate_age))
+        assert_equal(300, logger.instance_variable_get(:@rotate_size))
+      end
+    end
+  end
+
   def test_inline_config
     omit 'this feature is deprecated. see https://github.com/fluent/fluentd/issues/2711'