Ignore default_path test cases for Ruby with custom configuration

test/rubygems/test_gem.rb

@@ -577,6 +577,8 @@ def test_self_default_exec_format_jruby
   end
 
   def test_default_path
+    original_gem_default_path?
+
     vendordir(File.join(@tempdir, "vendor")) do
       FileUtils.rm_rf Gem.user_home
 
@@ -587,6 +589,8 @@ def test_default_path
   end
 
   def test_default_path_missing_vendor
+    original_gem_default_path?
+
     vendordir(nil) do
       FileUtils.rm_rf Gem.user_home
 
@@ -597,6 +601,8 @@ def test_default_path_missing_vendor
   end
 
   def test_default_path_user_home
+    original_gem_default_path?
+
     vendordir(File.join(@tempdir, "vendor")) do
       expected = [Gem.user_dir, Gem.default_dir]
 
@@ -605,6 +611,8 @@ def test_default_path_user_home
   end
 
   def test_default_path_vendor_dir
+    original_gem_default_path?
+
     vendordir(File.join(@tempdir, "vendor")) do
       FileUtils.mkdir_p Gem.vendor_dir
 
@@ -1799,4 +1807,10 @@ def util_remove_interrupt_command
   def util_cache_dir
     File.join Gem.dir, "cache"
   end
+
+  def original_gem_default_path?
+    unless Gem.method(:default_path).source_location.first.match? "lib/rubygems/defaults.rb"
+      pend "Gem.default_path likely differs from original RubyGems implementation"
+    end
+  end
 end