[rubygems/rubygems] Disallow warnings to creep into the test suite

https://github.com/rubygems/rubygems/commit/694e6afee7

lib/rubygems/test_case.rb

@@ -289,6 +289,10 @@ class Gem::TestCase < Minitest::Test
   # or <tt>i686-darwin8.10.1</tt> otherwise.
 
   def setup
+    @orig_stderr = $stderr.dup
+    @captured_stderr = Tempfile.new("captured_stderr")
+    $stderr.reopen @captured_stderr
+
     @orig_env = ENV.to_hash
     @tmp = File.expand_path("tmp")
 
@@ -462,6 +466,16 @@ class Gem::TestCase < Minitest::Test
     end
 
     @back_ui.close
+
+    $stderr.rewind
+    err = @captured_stderr.read
+    assert_empty err
+  ensure
+    @captured_stderr.unlink
+
+    $stderr.reopen @orig_stderr
+    @orig_stderr.close
+    @captured_stderr.close
   end
 
   def credential_setup