Exception raised when Kernel.system fails to execute a command

[rickr]

I've got an intermittent failure running my tests. When this occurs guard explodes in glorious fashion with the attached stack trace.

This is happening on a Mac Book Pro:
Darwin res-mppi6 15.6.0 Darwin Kernel Version 15.6.0: Mon Jan 9 23:07:29 PST 2017; root:xnu-3248.60.11.2.1~1/RELEASE_X86_64 x86_64

Under the following ruby:
ruby 2.2.5p319 (2016-04-26 revision 54774) [x86_64-darwin15]

This looks like it's due to Kernel.system being able to return true, false, or nil and the runner only checking for nil per the docs. It looks like the exception in run is trying to catch ENOENT but that returns false as well.

You can see this in action here:

[1] pry(main)> Kernel.system('echo $((1 / 1))')
1
=> true
[2] pry(main)> Kernel.system('echo $((1 / 0))')
sh: 1 / 0: division by 0 (error token is "0")
=> false
[3] pry(main)> Kernel.system('cat file_dun_exist')
cat: file_dun_exist: No such file or directory
=> false

Stack trace:

14:01:06 - ERROR - Guard::Minitest failed to achieve its <run_on_modifications>, exception was:
> [#] NoMethodError: undefined method `zero?' for nil:NilClass
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-minitest-2.4.6/lib/guard/minitest/runner.rb:66:in `run'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-minitest-2.4.6/lib/guard/minitest/runner.rb:85:in `run_on_modifications'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-minitest-2.4.6/lib/guard/minitest.rb:37:in `block in run_on_modifications'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-minitest-2.4.6/lib/guard/minitest.rb:51:in `throw_on_failed_tests'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-minitest-2.4.6/lib/guard/minitest.rb:37:in `run_on_modifications'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:83:in `block (2 levels) in _supervise'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/ui/config.rb:62:in `block in with_progname'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/lumberjack-1.0.11/lib/lumberjack/logger.rb:270:in `push_thread_local_value'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/lumberjack-1.0.11/lib/lumberjack/logger.rb:231:in `set_progname'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/ui/config.rb:61:in `with_progname'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:81:in `block in _supervise'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:79:in `catch'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:79:in `_supervise'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:61:in `block (3 levels) in run_on_changes'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:56:in `each'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:56:in `block (2 levels) in run_on_changes'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:121:in `block (2 levels) in _run_group_plugins'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:119:in `each'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:119:in `block in _run_group_plugins'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:118:in `catch'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:118:in `_run_group_plugins'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:54:in `block in run_on_changes'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:53:in `each'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/runner.rb:53:in `run_on_changes'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/internals/queue.rb:24:in `process'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/commander.rb:43:in `start'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/cli/environments/valid.rb:16:in `start_guard'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/cli.rb:122:in `start'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/thor-0.19.4/lib/thor/command.rb:27:in `run'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/thor-0.19.4/lib/thor/invocation.rb:126:in `invoke_command'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/thor-0.19.4/lib/thor.rb:369:in `dispatch'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/thor-0.19.4/lib/thor/base.rb:444:in `start'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/aruba_adapter.rb:32:in `execute'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/lib/guard/aruba_adapter.rb:19:in `execute!'
> [#] /Users/rickr/.rvm/gems/ruby-2.2.5@project/gems/guard-2.14.1/bin/_guard-core:11:in `<main>'

[rickr]

A little more investigating reveals that for whatever reason my tests are being terminated with signal 15. This still returns false and not nil. It looks like Open3 might behave the way that's expected. I also don't think raising ENOENT is the right thing to be raising.

PR coming shortly.