test(captcha): add a little test that verifies captcha works

check if all needed dependencies for captcha are installed

test/integration/default/controls/captcha_spec.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+control 'captcha generation' do
+  impact 0.5
+  title 'should be working'
+
+  # example captcha command generated by simple_captcha2 gem
+  captcha_cmd = 'convert -fill darkgreen -background white -size 120x20 -wave 1x96 '\
+    '-gravity Center -pointsize 22 -implode 0.2 label:01234 jpeg:-'
+
+  describe command(captcha_cmd) do
+    its('stderr') { should eq '' }
+    its('exit_status') { should eq 0 }
+  end
+end