Ruby: add specs for method KernAux.cmdline

pkgs/ruby/spec/lib/kernaux/cmdline_spec.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe KernAux, '.cmdline' do
+  subject(:cmdline) { described_class.cmdline str }
+
+  let(:str) { 'foo bar\\ baz "car cdr"' }
+
+  it { is_expected.to be_instance_of Array }
+  it { is_expected.to be_frozen }
+  it { is_expected.to all be_instance_of String }
+  it { is_expected.to all be_frozen }
+  it { is_expected.to eq ['foo', 'bar baz', 'car cdr'] }
+end