Avoid duplicates in path config

 - removed duplicate in path config
 - added testcase

Signed-off-by: Vimal Kumar <vimal78@gmail.com>

lib/fluent/plugin/in_tail.rb

@@ -136,7 +136,7 @@ def configure(conf)
         raise Fluent::ConfigError, "#{rc} are reserved words: #{@path_delimiter}"
       end
 
-      @paths = @path.split(@path_delimiter).map(&:strip)
+      @paths = @path.split(@path_delimiter).map(&:strip).sort().uniq()
       if @paths.empty?
         raise Fluent::ConfigError, "tail: 'path' parameter is required on tail input"
       end

test/plugin/test_in_tail.rb

@@ -102,6 +102,12 @@ def create_driver(conf = SINGLE_LINE_CONFIG, use_common_conf = true)
       assert_equal ["tail.txt", "test2", "tmp,dev"], d.instance.paths
     end
 
+    test "multi paths with same path configured twice" do
+      c = config_element("ROOT", "", { "path" => "test1.txt,test1.txt", "tag" => "t1", "path_delimiter" => "," })
+      d = create_driver(c + PARSE_SINGLE_LINE_CONFIG, false)
+      assert_equal ["test1.txt"], d.instance.paths
+    end
+
     test "multi paths with invaid path_delimiter" do
       c = config_element("ROOT", "", { "path" => "tail.txt|test2|tmp,dev", "tag" => "t1", "path_delimiter" => "*" })
       assert_raise(Fluent::ConfigError) do