brew test tests a given Formula Failure/Error: expect { brew "test", "--verbose", "testball" } .to output(/Testing testball/).to_stdout .and not_to_output.to_stderr .and be_a_success expected block to not output to stderr, but output "/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/bundle/ruby/2.6.0/gems/simplecov-0.22.0/lib/simplecov/lines_classifier.rb:36:in `foreach': No such file or directory @ rb_sysopen - /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/cmd/rbcmd.rb (Errno::ENOENT)\n\tfrom /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/bundle/ruby/2.6.0/gems/simplecov-0.22.0/lib/simplecov/lines_classifier.rb:36:in `each'\n\tfrom /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/bundle/ruby/2.6.0/gems/simplecov-0.22.0/lib/simplecov/lines_classifier.rb:36:in `map'\n\tfrom /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/bundle/ruby/2.6.0/gems/simplecov-0.22.0/lib/simplecov/lines_classifier.rb:36:in `classify'\n\tfrom /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/bundle/ruby/2.6.0/gems/simplecov-0.22.0/lib/simplecov/simulate_coverage.rb:22:in `call'\n\tfrom /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/.simplecov:43:in `block (3 levels) in <top (required)>'\n\tfrom /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/.simplecov:41:in `each'\n\tfrom /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/.simplecov:41:in `block (2 levels) in <top (required)>'\n\tfrom /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/bundle/ruby/2.6.0/gems/simplecov-0.22.0/lib/simplecov.rb:189:in `run_exit_tasks!'\n\tfrom /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/bundle/ruby/2.6.0/gems/simplecov-0.22.0/lib/simplecov.rb:179:in `at_exit_behavior'\n\tfrom /home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/vendor/bundle/ruby/2.6.0/gems/simplecov-0.22.0/lib/simplecov/defaults.rb:30:in `block in <top (required)>'\n" ...and: expected #<Proc:0x00005622883b1a90@/home/linuxbrew/.linuxbrew/Homebrew/Library/Homebrew/test/dev-cmd/test_spec.rb:15> to be a success