RubyGems provides means to override their defaults, such as
`Gem.default_path` method. With such modified configuration, the
following errors might be observed:
~~~
1) Failure:
TestGem#test_default_path_vendor_dir [/home/runner/work/ruby/ruby/src/test/rubygems/test_gem.rb:612]:
<["/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-qs43ch/gemhome",
"/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-qs43ch/vendor/gems/3.3.0+0"]> expected but was
<["/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-qs43ch/gemhome",
"/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-qs43ch/vendor/gems/3.3.0+0",
"/usr/local/lib/ruby/bundled_gems/3.3.0+0",
"/usr/local/lib/ruby/default_gems/3.3.0+0"]>.
make: *** [uncommon.mk:943: yes-test-all] Error 4
2) Failure:
TestGem#test_default_path_missing_vendor [/home/runner/work/ruby/ruby/src/test/rubygems/test_gem.rb:592]:
<["/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-c41yb7/gemhome"]> expected but was
<["/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-c41yb7/gemhome",
"/usr/local/lib/ruby/bundled_gems/3.3.0+0",
"/usr/local/lib/ruby/default_gems/3.3.0+0"]>.
3) Failure:
TestGem#test_default_path_user_home [/home/runner/work/ruby/ruby/src/test/rubygems/test_gem.rb:600]:
<["/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-5mm6uc/userhome/.local/share/gem/ruby/3.3.0+0",
"/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-5mm6uc/gemhome"]> expected but was
<["/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-5mm6uc/userhome/.local/share/gem/ruby/3.3.0+0",
"/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-5mm6uc/gemhome",
"/usr/local/lib/ruby/bundled_gems/3.3.0+0",
"/usr/local/lib/ruby/default_gems/3.3.0+0"]>.
4) Failure:
TestGem#test_default_path [/home/runner/work/ruby/ruby/src/test/rubygems/test_gem.rb:582]:
<["/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-kan9o5/gemhome"]> expected but was
<["/home/runner/work/ruby/ruby/build/tmp/test_rubygems_20231110-59661-kan9o5/gemhome",
"/usr/local/lib/ruby/bundled_gems/3.3.0+0",
"/usr/local/lib/ruby/default_gems/3.3.0+0"]>.
~~~
Of course the `Gem.default_path` could be stubbed, but testing stub
should not be the point.
Therefore, just detect if `Gem.default_path` was customized and ignore
the test cases.