kwargs-test.rb

require 'awesome_print'

class Foo
  def test(**kwargs)
    ap kwargs
  end

  def self.tester(label, &block)
    STDERR.printf "%12s: ", label
    begin
      block.call
      warn "--> ok"
    rescue ArgumentError
      warn "--> ArgumentError"
    end
  end
end

kwargs = { a: 5, b: 6}
foo = Foo.new
Foo.tester("simple args")  { foo.test(a: 1, b: 2) }
Foo.tester("hash arg")     { foo.test({a: 3, b: 4}) }
Foo.tester("hash arg var") { foo.test(kwargs) }
Foo.tester("splat args")   { foo.test(**kwargs) }

run-kwargs-test.out

$ rbenv shell 2.7.5
$ ruby --version
ruby 2.7.5p203 (2021-11-24 revision f69aeb8314) [x86_64-darwin21]
$ ruby kwargs-test.rb >/dev/null
 simple args: --> ok
    hash arg: --> ok
hash arg var: --> ok
  splat args: --> ok

$ rbenv shell 3.1.0
$ ruby --version
ruby 3.1.0p0 (2021-12-25 revision fb4df44d16) [x86_64-darwin21]
$ ruby kwargs-test.rb >/dev/null
 simple args: --> ok
    hash arg: --> ArgumentError
hash arg var: --> ArgumentError
  splat args: --> ok