Returning enums in ReferenceFilter#each_node

This changes ReferenceFilter#each_node so that when it's called without
a block an Enumerator is returned.

lib/banzai/filter/reference_filter.rb

@@ -68,6 +68,8 @@ module Banzai
       # by `ignore_ancestor_query`. Link tags are not processed if they have a
       # "gfm" class or the "href" attribute is empty.
       def each_node
+        return to_enum(__method__) unless block_given?
+
         query = %Q{descendant-or-self::text()[not(#{ignore_ancestor_query})]
         | descendant-or-self::a[
           not(contains(concat(" ", @class, " "), " gfm ")) and not(@href = "")

spec/lib/banzai/filter/reference_filter_spec.rb

+require 'spec_helper'
+
+describe Banzai::Filter::ReferenceFilter, lib: true do
+  let(:project) { build(:project) }
+
+  describe '#each_node' do
+    it 'iterates over the nodes in a document' do
+      document = Nokogiri::HTML.fragment('<a href="foo">foo</a>')
+      filter = described_class.new(document, project: project)
+
+      expect { |b| filter.each_node(&b) }.
+        to yield_with_args(an_instance_of(Nokogiri::XML::Element))
+    end
+
+    it 'returns an Enumerator when no block is given' do
+      document = Nokogiri::HTML.fragment('<a href="foo">foo</a>')
+      filter = described_class.new(document, project: project)
+
+      expect(filter.each_node).to be_an_instance_of(Enumerator)
+    end
+
+    it 'skips links with a "gfm" class' do
+      document = Nokogiri::HTML.fragment('<a href="foo" class="gfm">foo</a>')
+      filter = described_class.new(document, project: project)
+
+      expect { |b| filter.each_node(&b) }.not_to yield_control
+    end
+
+    it 'skips text nodes in pre elements' do
+      document = Nokogiri::HTML.fragment('<pre>foo</pre>')
+      filter = described_class.new(document, project: project)
+
+      expect { |b| filter.each_node(&b) }.not_to yield_control
+    end
+  end
+end