Add a test to assert rotate size

test/test_log.rb

@@ -445,6 +445,36 @@ def test_log_with_logdevio(expected)
     end
   end
 
+  def test_log_rotates_specifed_size_with_logdevio
+    with_timezone('utc') do
+      rotate_age = 2
+      rotate_size = 100
+      path = "#{TMP_DIR}/log-dev-io-#{rotate_size}-#{rotate_age}"
+
+      logdev = Fluent::LogDeviceIO.new(path, shift_age: rotate_age, shift_size: rotate_size)
+      logger = ServerEngine::DaemonLogger.new(logdev)
+      log = Fluent::Log.new(logger)
+
+      msg = 'a' * 101
+      log.info msg
+      assert_match msg, File.read(path)
+
+      # create log.0
+      msg2 = 'b' * 101
+      log.info msg2
+      c = File.read(path)
+      c0 = File.read(path + '.0')
+      assert_match msg2, c
+      assert_match msg, c0
+
+      # rotate
+      msg3 = 'c' * 101
+      log.info msg3
+      c = File.read(path)
+      c0 = File.read(path + '.0')
+      assert_match msg3, c
+      assert_match msg2, c0
+    end
   end
 end