Double Splat

Captures all keyword arguments.
And stores/returns them as a hash with key/value pair..
For keyword paramters.

Double splat when used with keyword paramters works perfectly:#

def testing(a:, **b)
  p a
  p b
end

testing(a: "test", message: "this is a message")

# Output:
$ruby main.rb
"test"
{:message=>"this is a message"}

Double splat when used with positional parameters errors out:#

def testing(a, **b)
  p a
  p b
end

testing("test", "this is a message")

# Output:
$ruby main.rb
main.rb:1:in `testing': wrong number of arguments (given 2, expected 1) (ArgumentError)
    from main.rb:7:in `<main>'

Double splat when used with keyword paramters works perfectly:
Double splat when used with positional parameters errors out: