1 files changed, 23 insertions, 0 deletions
diff --git a/spec/ruby/core/struct/dup_spec.rb b/spec/ruby/core/struct/dup_spec.rb
new file mode 100644
index 0000000000..8b50c39014
--- /dev/null
+++ b/spec/ruby/core/struct/dup_spec.rb
@@ -0,0 +1,23 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+require_relative 'shared/dup'
+
+describe "Struct-based class#dup" do
+
+  it_behaves_like :struct_dup, :dup
+
+  # 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