JRuby 10.1 on Windows raises TypeError inside File.symlink (wincode
trips on a nil path), so any test that exercises Gem::Installer's
symlink branch fails to even install the gem. Real users avoid the
branch entirely because `gem install` goes through DependencyInstaller
which passes wrappers: true. Mirror that production default for the
test suite by monkey-patching Gem::Installer.at and .for_spec in
test helper.rb so every direct caller (including the many tests that
bypass the installer_test_case helpers) gets wrappers: true on the
JRuby/Windows combo. The few tests that explicitly want the symlink
branch already set `installer.wrappers = false`, which still
overrides.
https://github.com/ruby/rubygems/commit/88f5e29e62
Hiroshi SHIBATA
f649009337