当然我读了这个：
rspec testing throws Uninitialized constant Rails (NameError)
但我确信我的代码没有任何问题。
仅仅因为操作系统！ （线程？）
以下是运行rspec时的错误消息：
/home/user/testapp/spec/spec_helper.rb:26:in `block in <top (required)>': uninitialized constant Rails (NameError)
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core.rb:98:in `configure'
from /home/user/testapp/spec/spec_helper.rb:22:in `<top (required)>'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/2.3.0/rubygems/core_ext/kernel_require.rb:55:in `require'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/configuration.rb:1394:in `block in requires='
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/configuration.rb:1394:in `each'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/configuration.rb:1394:in `requires='
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/configuration_options.rb:112:in `block in process_options_into'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/configuration_options.rb:111:in `each'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/configuration_options.rb:111:in `process_options_into'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/configuration_options.rb:21:in `configure'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:99:in `setup'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:86:in `run'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:71:in `run'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/lib/rspec/core/runner.rb:45:in `invoke'
from /home/user/.rbenv/versions/2.3.1/lib/ruby/gems/2.3.0/gems/rspec-core-3.5.4/exe/rspec:4:in `<top (required)>'
from /home/user/.rbenv/versions/2.3.1/bin/rspec:23:in `load'
from /home/user/.rbenv/versions/2.3.1/bin/rspec:23:in `<main>'
spec_helper文件的L26是：
Rails.application.env_config['action_dispatch.show_detailed_exceptions'] = false