Add precision parameter validation

Author: cosmo0920

lib/fluent/plugin/filter_elasticsearch_timestamp_check.rb

@@ -9,6 +9,7 @@ class ElasticsearchTimestampCheckFilter < Filter
     def configure(conf)
       super
       require 'date'
+      raise Fluent::ConfigError, "specify 1 or bigger number." if subsecond_precision < 1
       @strftime_format = "%Y-%m-%dT%H:%M:%S.%#{@subsecond_precision}N%z".freeze
     end
 

test/plugin/test_filter_elasticsearch_timestamp_check.rb

@@ -9,6 +9,18 @@ def create_driver(conf='')
     Fluent::Test::Driver::Filter.new(Fluent::Plugin::ElasticsearchTimestampCheckFilter).configure(conf)
   end
 
+  def test_configure
+    assert_raise(Fluent::ConfigError) do
+      create_driver(%[subsecond_precision -3])
+    end
+    assert_raise(Fluent::ConfigError) do
+      create_driver(%[subsecond_precision 0])
+    end
+    assert_nothing_raised do
+      create_driver(%[subsecond_precision 1])
+    end
+  end
+
   def test_added_timestamp
     d = create_driver
     d.run(default_tag: 'test') do