Prepare setup for *actual* following support.

The previous commit was nonsense as I didn't understand XPath's "following" axis
properly. This commit introduces proper tests and a note for future me so that I
can implement it properly.

lib/oga/xpath/evaluator.rb

@@ -254,17 +254,13 @@ module Oga
         context.each do |context_node|
           current = context_node
 
-          while current.respond_to?(:next)
-            next_node = current.next
-
-            if can_match_node?(next_node) and node_matches?(next_node, node)
-              nodes << next_node
-            end
-
-            # When this returns nil the loop automaticall breaks since `nil`
-            # doesn't respond to `next`.
-            current = next_node
-          end
+          # TODO: implement me properly this time.
+          #
+          # Step 1: gather *all* the nodes that come after the current node,
+          # regardless of their nesting.
+          #
+          # Step 2: compare all those nodes with the given test, only return
+          # those that match.
         end
 
         return nodes

spec/oga/xpath/evaluator/axes/following_spec.rb

@@ -3,45 +3,65 @@ require 'spec_helper'
 describe Oga::XPath::Evaluator do
   context 'following axis' do
     before do
-      document   = parse('<a><b></b><c></c><c></c></a>')
+      # Strip whitespace so it's easier to retrieve/compare elements.
+      @document = parse(<<-EOF.strip.gsub(/\s+/m, ''))
+<root>
+  <foo>
+    <bar></bar>
+    <baz>
+      <baz></baz>
+    </baz>
+  </foo>
+  <baz></baz>
+</root>
+      EOF
 
-      @first_c   = document.children[0].children[1]
-      @second_c  = document.children[0].children[2]
-      @evaluator = described_class.new(document)
+      @first_baz  = @document.children[0].children[1]
+      @second_baz = @first_baz.children[0]
+      @third_baz  = @document.children[0].children[0].children[1]
+      @evaluator  = described_class.new(@document)
     end
 
     # This should return an empty set since the document doesn't have any
     # following nodes.
     context 'using a document as the root' do
       before do
-        @set = @evaluator.evaluate('following::a')
+        @set = @evaluator.evaluate('following::foo')
       end
 
       it_behaves_like :empty_node_set
     end
 
-    context 'matching following elements using a name' do
+    context 'matching nodes in the current context' do
       before do
-        @set = @evaluator.evaluate('a/b/following::c')
+        @set = @evaluator.evaluate('root/foo/following::baz')
       end
 
-      it_behaves_like :node_set, :length => 2
+      it_behaves_like :node_set, :length => 1
 
-      example 'return the first <c> node' do
-        @set[0].should == @first_c
-      end
-
-      example 'return the second <c> node' do
-        @set[1].should == @second_c
+      example 'return the second <baz> node' do
+        @set[0].should == @first_baz
       end
     end
 
-    context 'matching following elements using a wildcard' do
+    context 'matching nodes in other contexts' do
       before do
-        @set = @evaluator.evaluate('a/b/following::*')
+        @set = @evaluator.evaluate('root/foo/bar/following::baz')
       end
 
-      it_behaves_like :node_set, :length => 2
+      it_behaves_like :node_set, :length => 3
+
+      example 'return the first <baz> node' do
+        @set[0].should == @first_baz
+      end
+
+      example 'return the second <baz> node' do
+        @set[1].should == @second_baz
+      end
+
+      example 'return the third <baz> node' do
+        @set[2].should == @third_baz
+      end
     end
   end
 end