Issue #12541 has been reported by Kazuhiro NISHIYAMA.

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Bug #12541: test failure with `umask 027`
https://bugs.ruby-lang.org/issues/12541

* Author: Kazuhiro NISHIYAMA
* Status: Open
* Priority: Normal
* Assignee: 
* ruby -v: ruby -v: ruby 2.4.0dev (2016-07-02 trunk 55562) [x86_64-linux]
* Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
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`ruby -e 'system("make", "test-all", "TESTS=fileutils/test_fileutils.rb",umask: 027)'` などのように `umask 027` の環境で実行すると TestFileUtils#test_cp_preserve_permissions が failure になります。

~~~
[31/91] TestFileUtils#test_cp_preserve_permissions = 0.00 s
  1) Failure:
TestFileUtils#test_cp_preserve_permissions [/home/vagrant/ruby/test/fileutils/test_fileutils.rb:286]:
File modes expected to be equal:
 <0755>: "tmp/cptmp"
 <0750>: "tmp/cptmp2"
~~~



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