1 files changed, 26 insertions, 0 deletions
diff --git a/test/ruby/test_file.rb b/test/ruby/test_file.rb
index 528193dabb..50f101867a 100644
--- a/test/ruby/test_file.rb
+++ b/test/ruby/test_file.rb
@@ -1,5 +1,6 @@
 require 'test/unit'
 require 'tempfile'
+require "thread"
 require_relative 'envutil'
 require_relative 'ut_eof'
 
@@ -118,6 +119,31 @@ class TestFile < Test::Unit::TestCase
     }
   end
 
+  def test_truncate_size
+    Tempfile.create("test-truncate") do |f|
+      q1 = Queue.new
+      q2 = Queue.new
+
+      Thread.new do
+        data = ''
+        64.times do |i|
+          data << i.to_s
+          f.rewind
+          f.print data
+          f.truncate(data.bytesize)
+          q1.push data.bytesize
+          q2.pop
+        end
+        q1.push nil
+      end
+
+      while size = q1.pop
+        assert_equal size, File.size(f.path)
+        q2.push true
+      end
+    end
+  end
+
   def test_read_all_extended_file
     [nil, {:textmode=>true}, {:binmode=>true}].each do |mode|
       Tempfile.create("test-extended-file", mode) {|f|