test_supervisor: add test case

Signed-off-by: Shizuo Fujita <fujita@clear-code.com>

Author: Watson1978

test/test_supervisor.rb

@@ -1168,6 +1168,72 @@ def test_stop_parallel_old_supervisor_after_delay
       expected = [c].concat(sources.collect { |type| {"@type" => type} })
       assert_equal(expected, supervisor.instance_variable_get(:@conf).elements)
     end
+
+    test "prevent duplicate loading" do
+      write_config("#{@config_include_dir}/system.conf", <<~EOF)
+        <system>
+          config_include_dir #{@config_include_dir}
+        </system>
+      EOF
+      write_config("#{@config_include_dir}/forward.conf", <<~EOF)
+        <match test>
+          @type forward
+          <buffer>
+            @include #{@config_include_dir}/common_param.conf
+          </buffer>
+          <server>
+            host 127.0.0.1
+            port 24224
+          </server>
+        </match>
+      EOF
+      write_config("#{@config_include_dir}/common_param.conf", <<~EOF)
+        flush_interval 5s
+      EOF
+      write_config("#{@config_include_dir}/obsolete_plugins.conf", <<~EOF)
+        <source>
+          @type obsolete_plugins
+        </source>
+      EOF
+
+      write_config("#{@tmp_dir}/fluent.conf", <<~EOF)
+        <match sample.*>
+          @type file
+          <buffer>
+            @include #{@config_include_dir}/common_param.conf
+          </buffer>
+        </match>
+
+        @include #{@config_include_dir}/forward.conf
+        @include #{@config_include_dir}/system.conf
+      EOF
+
+      supervisor = Fluent::Supervisor.new({ config_path: "#{@tmp_dir}/fluent.conf" })
+      supervisor.configure(supervisor: true)
+      elements = supervisor.instance_variable_get(:@conf).elements
+      assert_equal(4, elements.size)
+
+      assert_equal('match', elements[0].name)
+      assert_equal('file', elements[0]['@type'])
+      assert_equal('buffer', elements[0].elements[0].name)
+      assert_equal('5s', elements[0].elements[0]['flush_interval'])
+
+      assert_equal('match', elements[1].name)
+      assert_equal('forward', elements[1]['@type'])
+      assert_equal('buffer', elements[1].elements[0].name)
+      assert_equal('5s', elements[1].elements[0]['flush_interval'])
+
+      assert_equal('system', elements[2].name)
+      assert_equal(@config_include_dir, elements[2]['config_include_dir'])
+
+      assert_equal('source', elements[3].name)
+      assert_equal('obsolete_plugins', elements[3]['@type'])
+
+      # reload
+      supervisor.__send__(:reload_config)
+      reload_elements = supervisor.instance_variable_get(:@conf).elements
+      assert_equal(elements, reload_elements)
+    end
   end
 
   def create_debug_dummy_logger