init.pp

class kp_ls(
  #$somevar = $kp_ls::params::somevar,
  #$somevar1 = $kp_ls::params::somevar1,
) inherits kp_ls::params {
  notify { 'foo': }
  notify { 'foo1': message => hiera('foo_message') }
}

init_spec.rb

require 'spec_helper'

describe 'kp_ls', :type => :class do
    let(:node) { 'testhost.example.com' }

    let(:hiera_config) do
        { :backends => ['yaml'],
            :hierarchy => [
                '%{fqdn}/%{fqdn}',
                '%{fqdn}/%{calling_module}',
                '%{calling_module}',
            ],
                :yaml => {
            :datadir => File.expand_path(File.join(__FILE__, '..', '..', '..', 'hieradata')) }}
    end

    it { should compile }
    it { should compile.with_all_deps }
    it { should contain_notify('foo') }

    #let(:hiera_data) { { :foo_message => "bar" } }

    it { should contain_notify("foo1").with_message("bar") }
end

params.pp

class kp_ls::params() {
  $somevar = 1
  $somevar1 = 2
}

spec_results_fails

FFFF

Failures:

  1) kp_ls
     Failure/Error: it { should compile }
     Puppet::Error:
       Error from DataBinding 'hiera' while looking up 'kp_ls::somevar': FileSystem implementation expected Pathname, got: 'Hash' on node testhost.example.com
     # ./spec/classes/init_spec.rb:17:in `block (2 levels) in <top (required)>'

  2) kp_ls
     Failure/Error: it { should compile.with_all_deps }
     Puppet::Error:
       Error from DataBinding 'hiera' while looking up 'kp_ls::somevar': FileSystem implementation expected Pathname, got: 'Hash' on node testhost.example.com
     # ./spec/classes/init_spec.rb:18:in `block (2 levels) in <top (required)>'

  3) kp_ls
     Failure/Error: it { should contain_notify('foo') }
     Puppet::Error:
       Error from DataBinding 'hiera' while looking up 'kp_ls::somevar': FileSystem implementation expected Pathname, got: 'Hash' on node testhost.example.com
     # ./spec/classes/init_spec.rb:19:in `block (2 levels) in <top (required)>'

  4) kp_ls
     Failure/Error: it { should contain_notify("foo1").with_message("bar") }
     Puppet::Error:
       Error from DataBinding 'hiera' while looking up 'kp_ls::somevar': FileSystem implementation expected Pathname, got: 'Hash' on node testhost.example.com
     # ./spec/classes/init_spec.rb:23:in `block (2 levels) in <top (required)>'

4 deprecations logged to a.txt

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4 examples, 4 failures

did you get anywhere with this? i am having the same problems.