Add support for pre_condition with functions

This commit adds support for using the pre_condition
hook to specify the source code that should be used to
compile a catalog that can be introspected by functions for
testing purposes.

This allows users to test functions that need access to
catalog contents.

This allows the following snippet to test a function that
needs access to the catalog generated by pre_condition:

  describe 'defined_with_params' do
    #describe 'when resource is passed as a string' do
    let :pre_condition do
      'user { "dan": }'
    end
    it { should run.with_params('User[dan]', {}).and_return('true') }
  end

lib/rspec-puppet/example/function_example_group.rb

@@ -9,9 +9,36 @@ def subject
       Puppet[:libdir] = Dir["#{Puppet[:modulepath]}/*/lib"].entries.join(File::PATH_SEPARATOR)
       Puppet::Parser::Functions.autoloader.loadall
 
-      scope = Puppet::Parser::Scope.new
+      # if we specify a pre_condition, we should ensure that we compile that code
+      # into a catalog that is accessible from the scope where the function is called
+      if self.respond_to? :pre_condition
+        Puppet[:code] = pre_condition
+        nodename = self.respond_to?(:node) ? node : Puppet[:certname]
+        facts_val = {
+          'hostname' => nodename.split('.').first,
+          'fqdn' => nodename,
+          'domain' => nodename.split('.').last,
+        }
+        facts_val.merge!(munge_facts(facts)) if self.respond_to?(:facts)
+        # we need to get a compiler, b/c we can attach that to a scope
+        @compiler = build_compiler(nodename, facts_val)
+      else
+        @compiler = nil
+      end
+
+      scope = Puppet::Parser::Scope.new(:compiler => @compiler)
 
       scope.method "function_#{function_name}".to_sym
     end
+
+    def compiler
+      @compiler
+    end
+    # get a compiler with an attached compiled catalog
+    def build_compiler(node_name, fact_values)
+      compiler = Puppet::Parser::Compiler.new(Puppet::Node.new(node_name, :parameters => fact_values))
+      compiler.compile
+      compiler
+    end
   end
 end