1 files changed, 15 insertions, 0 deletions
diff --git a/spec/ruby/library/stringio/shared/write.rb b/spec/ruby/library/stringio/shared/write.rb
index 0eb71466e3..c5a0f8f513 100644
--- a/spec/ruby/library/stringio/shared/write.rb
+++ b/spec/ruby/library/stringio/shared/write.rb
@@ -45,6 +45,21 @@ describe :stringio_write_string, shared: true do
     @io.pos.should eql(4)
   end
 
+  it "handles concurrent writes correctly" do
+    @io = StringIO.new
+    n = 8
+    go = false
+    threads = n.times.map { |i|
+      Thread.new {
+        Thread.pass until go
+        @io.write i.to_s
+      }
+    }
+    go = true
+    threads.each(&:join)
+    @io.string.size.should == n.times.map(&:to_s).join.size
+  end
+
   ruby_version_is ""..."3.0" do
     it "does not taint self when the passed argument is tainted" do
       @io.send(@method, "test".taint)