Merge pull request #3784 from fluent/output-more-info-of-unstable-test

test_in_tail: Show more information of test_unwatched_files_should_be_removed

test/plugin/test_in_tail.rb

@@ -1612,9 +1612,18 @@ def test_unwatched_files_should_be_removed
       waiting(20) { sleep 0.1 until Dir.glob("#{@tmp_dir}/*.txt").size == 0 } # Ensure file is deleted on Windows
       waiting(5) { sleep 0.1 until d.instance.instance_variable_get(:@tails).keys.size <= 0 }
 
-      assert_equal(0, d.instance.instance_variable_get(:@tails).keys.size)
-
-      d.instance_shutdown
+      assert_equal(
+        {
+          files: [],
+          tails: {}
+        },
+        {
+          files: Dir.glob("#{@tmp_dir}/*.txt"),
+          tails: d.instance.instance_variable_get(:@tails)
+        }
+      )
+    ensure
+      d.instance_shutdown if d && d.instance
     end
 
     def count_timer_object