in_tail: thread_pool: Add tailing thread poll testcases

Signed-off-by: Hiroshi Hatake <hatake@clear-code.com>

test/plugin/in_tail/test_tailthread_pool.rb

@@ -0,0 +1,26 @@
+require_relative '../../helper'
+require 'fluent/plugin/in_tail'
+
+class TailThreadPoolTest < Test::Unit::TestCase
+  data("single thread" => 1,
+       "max thread pool size (10)" => 10,
+       "max thread pool size (20)" => 20,
+      )
+  test "thread pool creation" do |data|
+    max_threads_pool_size = data
+    thread_pool = Fluent::Plugin::TailInput::TailThread::Pool.new(max_threads_pool_size) do |pool|
+      100.times {|n|
+        pool.run {
+          nop_task(0.01)
+          assert do
+            pool.instance_variable_get(:@threads).size <= max_threads_pool_size
+          end
+        }
+      }
+    end
+  end
+
+  def nop_task(sleep_time)
+    sleep sleep_time
+  end
+end