Convert tests to use plain rspec-puppet

Tests in the new style produces the following documentation output:

abs
  should not eq nil
  should run abs() and raise an Puppet::ParseError
  should run abs(-34) and return 34
  should run abs("-34") and return 34
  should run abs(34) and return 34
  should run abs("34") and return 34

1 files changed, 18 insertions, 16 deletions

diff --git a/spec/functions/difference_spec.rb b/spec/functions/difference_spec.rb
index 24b2b1b..d5e983d 100755
--- a/spec/functions/difference_spec.rb
+++ b/spec/functions/difference_spec.rb
@@ -1,19 +1,21 @@
-#! /usr/bin/env ruby -S rspec
 require 'spec_helper'
 
-describe "the difference function" do
-  let(:scope) { PuppetlabsSpec::PuppetInternals.scope }
-
-  it "should exist" do
-    expect(Puppet::Parser::Functions.function("difference")).to eq("function_difference")
-  end
-
-  it "should raise a ParseError if there are fewer than 2 arguments" do
-    expect { scope.function_difference([]) }.to( raise_error(Puppet::ParseError) )
-  end
-
-  it "should return the difference between two arrays" do
-    result = scope.function_difference([["a","b","c"],["b","c","d"]])
-    expect(result).to(eq(["a"]))
-  end
+describe 'difference' do
+  it { is_expected.not_to eq(nil) }
+  it { is_expected.to run.with_params().and_raise_error(Puppet::ParseError) }
+  it { is_expected.to run.with_params('one').and_raise_error(Puppet::ParseError) }
+  it { is_expected.to run.with_params('one', 'two').and_raise_error(Puppet::ParseError) }
+  it { is_expected.to run.with_params('one', 'two', 'three').and_raise_error(Puppet::ParseError) }
+  it { is_expected.to run.with_params('one', []).and_raise_error(Puppet::ParseError) }
+  it { is_expected.to run.with_params([], 'two').and_raise_error(Puppet::ParseError) }
+  it { is_expected.to run.with_params({}, {}).and_raise_error(Puppet::ParseError) }
+  it { is_expected.to run.with_params([], []).and_return([]) }
+  it { is_expected.to run.with_params([], ['one']).and_return([]) }
+  it { is_expected.to run.with_params(['one'], ['one']).and_return([]) }
+  it { is_expected.to run.with_params(['one'], []).and_return(['one']) }
+  it { is_expected.to run.with_params(['one', 'two', 'three'], ['two', 'three']).and_return(['one']) }
+  it { is_expected.to run.with_params(['one', 'two', 'two', 'three'], ['two', 'three']).and_return(['one']) }
+  it { is_expected.to run.with_params(['one', 'two', 'three'], ['two', 'two', 'three']).and_return(['one']) }
+  it { is_expected.to run.with_params(['one', 'two', 'three'], ['two', 'three', 'four']).and_return(['one']) }
+  it 'should not confuse types' do is_expected.to run.with_params(['1', '2', '3'], [1, 2]).and_return(['1', '2', '3']) end
 end