How to enable logging for custom layouts?

[SoftBoil]

I would like to output Javascript console messages to better understand creating custom layouts.

I saw another Q&A that references a merged change to enable console logging to a file.  In the discussion it said to use Amethyst with a "--log" argument.

I tried running this in "~/Applications/Amethyst.app/Contents/MacOS" but get an error:

./Amethyst --log ~/test.log
Error: Unknown option '--log'
Usage: amethyst app
  See 'amethyst app --help' for more information.

./Amethyst app --log ~/test.log gives the same error.
 And using open just silently exits:
open -a ~/Applications/Amethyst.app --args --log ~/test.log

Can someone provide some guidance please?