[ruby-cvs:78476] 409e4ab740 (master): tool/lib/test/unit/parallel.rb: fail explicitly when failing to get io

Yusuke Endoh	2019-12-03 17:05:07 +0900 (Tue, 03 Dec 2019)

  New Revision: 409e4ab740

  https://github.com/ruby/ruby/commit/409e4ab740

  Log:
    tool/lib/test/unit/parallel.rb: fail explicitly when failing to get io
    
    `(ulimit -n 30; make test-tool)` fails with unexplicit message:
    "undefined method `write' for nil:NilClass" due to lack of stdout.
    
    This change makes it explicit.  [Bug #5577]

  Modified files:
    tool/lib/test/unit/parallel.rb
    tool/test/testunit/test_parallel.rb