/install/lib/ruby/2.7.0/racc/statetransitiontable.rb:214:in `mkmapexp': can't modify frozen String: "" (FrozenError)
	/install/lib/ruby/2.7.0/racc/statetransitiontable.rb:184:in `addent'
	/install/lib/ruby/2.7.0/racc/statetransitiontable.rb:127:in `block in gen_action_tables'
	/install/lib/ruby/2.7.0/racc/state.rb:53:in `each'
	/install/lib/ruby/2.7.0/racc/state.rb:53:in `each_state'
	/install/lib/ruby/2.7.0/racc/statetransitiontable.rb:117:in `gen_action_tables'
	/install/lib/ruby/2.7.0/racc/statetransitiontable.rb:77:in `generate'
	/install/lib/ruby/2.7.0/racc/statetransitiontable.rb:40:in `generate'
	/install/lib/ruby/2.7.0/racc/state.rb:90:in `state_transition_table'
	/install/lib/ruby/2.7.0/racc/grammar.rb:148:in `parser_class'
	/install/lib/ruby/2.7.0/racc/grammarfileparser.rb:143:in `<module:Racc>'
	/install/lib/ruby/2.7.0/racc/grammarfileparser.rb:19:in `<top (required)>'
	/install/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	/install/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	/install/lib/ruby/2.7.0/racc/static.rb:3:in `<top (required)>'
	/install/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	/install/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	/ruby/test/racc/helper.rb:6:in `<top (required)>'
	/install/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	/install/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	/ruby/test/racc/test_chk_y.rb:1:in `<top (required)>'
	/install/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	/install/lib/ruby/2.7.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	/ruby/test/lib/test/unit/parallel.rb:116:in `run'
	/ruby/test/lib/test/unit/parallel.rb:207:in `<main>'
running file: /ruby/test/racc/test_chk_y.rb

Some worker was crashed. It seems ruby interpreter's bug
or, a bug of test/unit/parallel.rb. try again without -j
option.

9344:running:test_chk_y: Broken pipe

/ruby/test/net/ftp/test_ftp.rb: cannot load such file -- /ruby/test/net/utils (Test::Unit::ProxyError)