Set process title of parallelized test workers

[jhawthorn]

This sets the process title of the forked test workers in ActiveSupport::Testing::Parallelization.

This could help users to debug slow or hanging tests and provides a way to observe the running and progress of tests. But mostly, I think it's cool to watch inside top ⚡.

$ ps -o cmd= f
/bin/zsh
 \_ /home/jhawthorn/.gem/ruby/2.6.3/bin/rake test:template
     \_ /home/jhawthorn/github/github/vendor/ruby/300089b723cc69420cdbb406d27f5a2b8c4aef96/bin/ruby -w -Ilib:test -I/home/jhawthorn/.rubies/ruby-2.6.3/lib/ruby/gems/2.6.0/gems/rake-12.3.2/lib /home/jhawthorn/.rubies/ruby-2.6.3/lib/ruby/gem
         \_ Rails test worker 0 - FormTagHelperTest#test_submit_tag_with_symbol_value
         \_ Rails test worker 1 - CachedViewRenderTest#test_render_partial_with_errors
         \_ Rails test worker 2 - (idle)
         \_ Rails test worker 3 - OptimizedFileSystemResolverTest#test_doesnt_find_template_with_wrong_details
         \_ Rails test worker 4 - FormTagHelperTest#test_time_field_tag
         \_ Rails test worker 5 - FormTagHelperTest#test_field_set_tag_in_erb

I don't think Rails has previously used setproctitle anywhere. For web requests the web server will do this for us (puma and unicorn do at least). However, I think it makes sense here. Rails has forked these process and runs this loop for its entire lifetime.

[matthewd]

Is "Rails test worker" more verbose than we want to be? setproctitle only has the number of characters in the original commandline to play with, and not everyone's ruby path is quite that long. 😄

I'm also slightly torn between using the test class + method as you have (which is probably nicer to read at a glance), and suggesting we might use the filename:lineno instead, which you might want to copy to a new runner if you see a child process get stuck, say.

[jhawthorn]

setproctitle only has the number of characters in the original commandline to play with

Is this still a limitation on modern systems? Linux/BSDs implement setproctitle(3). AFAICT MacOS Mojave still relies on overwriting ARGV, but in my testing (Mojave/Ruby 2.6) I was able to set long titles using ruby -e '$0 = "a"*1000; sleep 4' 🤷‍♂. I'm open to making it shorter of course.

I'm also slightly torn between using the test class + method as you have (which is probably nicer to read at a glance), and suggesting we might use the filename:lineno instead, which you might want to copy to a new runner if you see a child process get stuck, say.

I chose "Class#method" to mirror running tests with --verbose, which is how I would previously (without parallelism) have detected which test would hang. Hopefully it's not a common enough problem to need to optimize developer experience for 😅