1 files changed, 20 insertions, 0 deletions
diff --git a/spec/rubyspec/core/struct/dup_spec.rb b/spec/rubyspec/core/struct/dup_spec.rb
new file mode 100644
index 0000000000..d1da31d6d5
--- /dev/null
+++ b/spec/rubyspec/core/struct/dup_spec.rb
@@ -0,0 +1,20 @@
+require File.expand_path('../../../spec_helper', __FILE__)
+require File.expand_path('../fixtures/classes', __FILE__)
+
+describe "Struct-based class#dup" do
+
+  # From https://github.com/jruby/jruby/issues/3686
+  it "retains an included module in the ancestor chain for the struct's singleton class" do
+    klass = Struct.new(:foo)
+    mod = Module.new do
+      def hello
+        "hello"
+      end
+    end
+
+    klass.extend(mod)
+    klass_dup = klass.dup
+    klass_dup.hello.should == "hello"
+  end
+
+end