specify prefix for Dir.mktmpdir.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@13765 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

test/pathname/test_pathname.rb

@@ -287,7 +287,7 @@ class TestPathname < Test::Unit::TestCase
       return
     rescue TypeError
     end
-    Dir.mktmpdir {|dir|
+    Dir.mktmpdir('rubytest-pathname') {|dir|
       File.symlink("not-exist-target", "#{dir}/not-exist")
       assert_raise(Errno::ENOENT) { realpath("#{dir}/not-exist") }
       File.symlink("loop", "#{dir}/loop")

test/ruby/test_dir.rb

@@ -6,7 +6,7 @@ require 'fileutils'
 class TestDir < Test::Unit::TestCase
 
   def setup
-    @root = Dir.mktmpdir
+    @root = Dir.mktmpdir('__test_dir__')
     for i in ?a..?z
       if i.ord % 2 == 0
         FileUtils.touch(File.join(@root, i))

test/ruby/test_file.rb

@@ -7,7 +7,7 @@ class TestFile < Test::Unit::TestCase
   # I don't know Ruby's spec about "unlink-before-close" exactly.
   # This test asserts current behaviour.
   def test_unlink_before_close
-    Dir.mktmpdir {|tmpdir|
+    Dir.mktmpdir('rubytest-file') {|tmpdir|
       filename = tmpdir + '/' + File.basename(__FILE__) + ".#{$$}"
       w = File.open(filename, "w")
       w << "foo"