merge revision(s) 56884,56892: [Backport #12910]

test_fileutils.rb: Use primary group too

	* test/fileutils/test_fileutils.rb (TestFileUtils#setup): Use
  primary group as well as supplementary groups.  based on the
  patch by Vit Ondruch at [ruby-core:78053].  [Bug #12910]

	It might happen in certain environments (systemd-nspawn) that
	process has no supplementary groups, but primary groups should be
	enough to pass most of the tests.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_2@57223 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/fileutils/test_fileutils.rb

@@ -17,8 +17,11 @@ class TestFileUtils < Test::Unit::TestCase
       fu.instance_variable_set(:@fileutils_output, write)
       th = Thread.new { read.read }
       th2 = Thread.new {
-        yield
-        write.close
+        begin
+          yield
+        ensure
+          write.close
+        end
       }
       th_value, _ = assert_join_threads([th, th2])
       lines = th_value.lines.map {|l| l.chomp }
@@ -136,7 +139,7 @@ class TestFileUtils < Test::Unit::TestCase
 
   def setup
     @prevdir = Dir.pwd
-    @groups = Process.groups if have_file_perm?
+    @groups = [Process.gid] | Process.groups if have_file_perm?
     tmproot = TMPROOT
     mymkdir tmproot unless File.directory?(tmproot)
     Dir.chdir tmproot
@@ -208,6 +211,16 @@ class TestFileUtils < Test::Unit::TestCase
   # Test Cases
   #
 
+  def test_assert_output_lines
+    assert_raise(MiniTest::Assertion) {
+      Timeout.timeout(0.1) {
+        assert_output_lines([]) {
+          raise "ok"
+        }
+      }
+    }
+  end
+
   def test_pwd
     check_singleton :pwd