Puppet users - Jul 2013 - rspec-puppet: how to pass undef as parameter value?

Hi all,

is there a way to pass the Puppets undef [1] value as parameter? I got a
module with a package_provider parameter, allowing the user two things:
1. specify a specific package provider to use; 2. pass "undef" to let
Puppet decide which provider to use instead of the module.

Something like:
> class example(
>   $package_provider = $example::params::package_provider,
> ) inherits example::params {
>
>   [...]
>
>   package { ''foobar''
>     ensure   => ''present'',
>     provider => $package_provider,
>   }
> }

Now I want to test if passing undef works:
> context ''with parameter(s): package_provider => undef''
do
>   let(:params) {{
>     :package_provider => [WAY-TO-PASS-UNDEF-HERE],
>   }}
> 
>   it ''contains a package with parameter(s): provider =>
unset'' do
>     should contain_package(''blueprint'').with({
>       ''provider'' => [WAY-TO-CHECK-FOR-UNDEF-HERE,
>     })
>   end
> end


But my test doesn''t work. What I tried so far is:

1) undef (results in RSpec/Ruby parsing error)
> context ''with parameter(s): foo => undef'' do
>   let(:params) {{
>     :foo => undef,
>   }}
>
>   [...]
> end
2) :undef (results in Puppet error: "Syntax error at'':'';
expected ''}''" )
> context ''with parameter(s): foo => undef'' do
>   let(:params) {{
>     :foo => :undef,
>   }}
>
>   [...]
> end
3) nil (does not result in an Puppet or Ruby error, but the
.with_foo(nil) or .without_foo matchers do not seem to work as the
string "nil" was passed tho puppet
> context ''with parameter(s): foo => undef'' do
>   let(:params) {{
>     :foo => nil,
>   }}
>
>   [...]
> end
Any hints? Thanks in advance :-)


[1]
<http://docs.puppetlabs.com/puppet/latest/reference/lang_datatypes.html#undef>

-- 
Andreas <http://blog.andreas-haerter.com>