rails test が実行できません。

Question

cloud 9を使っております。rails tutorial 8章が終了し、rails t を実行しようとしたのですが、下記が表示されて上手くいきません。

Traceback (most recent call last):
46: from -e:1:in <main>' 45: from /home/ubuntu/.rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in require'
44: from /home/ubuntu/.rvm/rubies/ruby-2.6.3/lib/ruby/2.6.0/rubygems/core_ext/kernel_require.rb:54:in require' 43: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/spring-2.1.0/lib/spring/application/boot.rb:19:in <top (required)>'
42: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/spring-2.1.0/lib/spring/application.rb:139:in run' 41: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/spring-2.1.0/lib/spring/application.rb:139:in loop'
40: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/spring-2.1.0/lib/spring/application.rb:145:in block in run' 39: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/spring-2.1.0/lib/spring/application.rb:175:in serve'
38: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/spring-2.1.0/lib/spring/application.rb:175:in fork' 37: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/spring-2.1.0/lib/spring/application.rb:215:in block in serve'
36: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/spring-2.1.0/lib/spring/command_wrapper.rb:38:in call' 35: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/spring-2.1.0/lib/spring/commands/rails.rb:6:in call'
34: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:55:in load' 33: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:55:in load'
32: from /home/ubuntu/environment/hello_app/bin/rails:9:in <main>' 31: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/zeitwerk-2.3.0/lib/zeitwerk/kernel.rb:23:in require'
30: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in require' 29: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in require_with_bootsnap_lfi'
28: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in register' 27: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in block in require_with_bootsnap_lfi'
26: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in require' 25: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/railties-6.0.2.2/lib/rails/commands.rb:18:in <main>'
24: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/railties-6.0.2.2/lib/rails/command.rb:46:in invoke' 23: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/railties-6.0.2.2/lib/rails/command/base.rb:69:in perform'
22: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/thor-1.0.1/lib/thor.rb:392:in dispatch' 21: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/thor-1.0.1/lib/thor/invocation.rb:127:in invoke_command'
20: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/thor-1.0.1/lib/thor/command.rb:27:in run' 19: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/railties-6.0.2.2/lib/rails/commands/test/test_command.rb:33:in perform'
18: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/railties-6.0.2.2/lib/rails/test_unit/runner.rb:39:in run' 17: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/railties-6.0.2.2/lib/rails/test_unit/runner.rb:50:in load_tests'
16: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/railties-6.0.2.2/lib/rails/test_unit/runner.rb:50:in each' 15: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/railties-6.0.2.2/lib/rails/test_unit/runner.rb:50:in block in load_tests'
14: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/zeitwerk-2.3.0/lib/zeitwerk/kernel.rb:23:in require' 13: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in require'
12: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in require_with_bootsnap_lfi' 11: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in register'
10: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in block in require_with_bootsnap_lfi' 9: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in require'
8: from /home/ubuntu/environment/hello_app/test/channels/application_cable/connection_test.rb:1:in <main>' 7: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/zeitwerk-2.3.0/lib/zeitwerk/kernel.rb:23:in require'
6: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:31:in require' 5: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in require_with_bootsnap_lfi'
4: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in register' 3: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in block in require_with_bootsnap_lfi'
2: from /home/ubuntu/.rvm/gems/ruby-2.6.3/gems/bootsnap-1.4.6/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:23:in require' 1: from /home/ubuntu/environment/hello_app/test/test_helper.rb:5:in <main>'
/home/ubuntu/environment/hello_app/test/test_helper.rb:13:in <class:TestCase>': undefined local variable or method 　' for ActiveSupport::TestCase:Class (NameError)

試したこと
springの再起動
code sampleと比較して文法ミス等のチェック
rails db:migrate

解決方法でなくても、こうしたらできるかも、というようなことでも良いのでお願い致します。

Answer 1

全フォルダのコメントを消去したら、実行できました。（理由は分かりません。。。）理由を知っている方がいらっしゃいましたら教えて頂けると幸いです。