Port Bundler's YAML serializer specs to the RubyGems test suite

The RubyGems test suite already covers almost all of the Bundler
yaml_serializer spec through test_gem_safe_yaml.rb. Port the two missing
cases (URL mapping keys as used by mirror settings, and Psych
interoperability in both directions) and drop the Bundler spec.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: hsbt

spec/bundler/yaml_serializer_spec.rb

@@ -42,7 +42,6 @@ module Shards
         "spec/bundler/env_spec.rb",
         "spec/install/gems/mirror_spec.rb",
         "spec/install/failure_spec.rb",
-        "spec/bundler/yaml_serializer_spec.rb",
         "spec/bundler/environment_preserver_spec.rb",
         "spec/install/gemfile/install_if_spec.rb",
         "spec/install/gems/gemfile_source_header_spec.rb",

spec/support/shards.rb

@@ -950,6 +950,45 @@ def test_roundtrip_empty_collections
     assert_equal({}, loaded["hash"])
   end
 
+  def test_load_url_key_and_value
+    # Bundler mirror settings use URLs both as mapping key and value
+    yaml = "BUNDLE_MIRROR__HTTPS://RUBYGEMS__ORG/: http://example-mirror.rubygems.org\n"
+
+    expected = { "BUNDLE_MIRROR__HTTPS://RUBYGEMS__ORG/" => "http://example-mirror.rubygems.org" }
+    assert_equal expected, yaml_load(yaml)
+  end
+
+  def test_psych_interop_roundtrip
+    require "yaml"
+
+    hash = {
+      "a_joke" => {
+        "my-stand" => "I can totally keep secrets",
+        "but" => "The people I tell them to can't :P",
+        "wouldn't it be funny if this string were empty?" => "",
+      },
+      "more" => {
+        "first" => [
+          "Can a kangaroo jump higher than a house?",
+          "Of course, a house doesn't jump at all.",
+        ],
+        "second" => [
+          "What did the sea say to the sand?",
+          "Nothing, it simply waved.",
+        ],
+        "array with empty string" => [""],
+      },
+      "sales" => {
+        "item" => "A Parachute",
+        "description" => "Only used once, never opened.",
+      },
+      "one-more" => "I'd tell you a chemistry joke but I know I wouldn't get a reaction.",
+    }
+
+    assert_equal hash, Gem::YAMLSerializer.load(Psych.dump(hash))
+    assert_equal hash, Psych.load(Gem::YAMLSerializer.dump(hash))
+  end
+
   def test_load_double_quoted_escape_sequences
     result = yaml_load("newline: \"hello\\nworld\"")
     assert_equal "hello\nworld", result["newline"]