[ruby/psych] Test that recursive refs dump as aliases

https://github.com/ruby/psych/commit/d9f7289190

test/psych/test_array.rb

@@ -57,6 +57,19 @@ module Psych
       assert_cycle(@list)
     end
 
+    def test_recursive_array_uses_alias
+      @list << @list
+
+      expected = <<~eoyaml
+        --- &1
+        - :a: b
+        - foo
+        - *1
+      eoyaml
+
+      assert_equal expected, Psych.dump(@list)
+    end
+
     def test_cycle
       assert_cycle(@list)
     end

test/psych/test_hash.rb

@@ -112,6 +112,18 @@ eoyml
       assert_equal({"foo"=>{"hello"=>"world"}, "bar"=>{"hello"=>"world"}}, hash)
     end
 
+    def test_recursive_hash_uses_alias
+      h = { }
+      h["recursive_reference"] = h
+
+      expected = <<~eoyaml
+        --- &1
+        recursive_reference: *1
+      eoyaml
+
+      assert_equal(expected, Psych.dump(h))
+    end
+
     def test_key_deduplication
       unless String.method_defined?(:-@) && (-("a" * 20)).equal?((-("a" * 20)))
         pend "This Ruby implementation doesn't support string deduplication"

test/psych/test_object.rb

@@ -41,5 +41,17 @@ module Psych
       assert_instance_of(Foo, loaded)
       assert_equal loaded, loaded.parent
     end
+
+    def test_cyclic_reference_uses_alias
+      foo = Foo.new(nil)
+      foo.parent = foo
+
+      expected = <<~eoyaml
+        --- &1 !ruby/object:Psych::Foo
+        parent: *1
+      eoyaml
+
+      assert_equal expected, Psych.dump(foo)
+    end
   end
 end