Added various failing following/preceding specs.

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

@@ -16,6 +16,7 @@ describe Oga::XPath::Evaluator do
 </root>
       EOF
 
+      @bar1 = @document.children[0].children[0].children[0]
       @baz1 = @document.children[0].children[0].children[1]
       @baz2 = @baz1.children[0]
       @baz3 = @document.children[0].children[1]
@@ -36,5 +37,9 @@ describe Oga::XPath::Evaluator do
       evaluate_xpath(@document, 'root/foo/bar/following-sibling::baz')
         .should == node_set(@baz1)
     end
+
+    example 'return a node set containing the siblings relative to root/foo/bar' do
+      evaluate_xpath(@bar1, 'following-sibling::baz').should == node_set(@baz1)
+    end
   end
 end

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

@@ -16,6 +16,7 @@ describe Oga::XPath::Evaluator do
 </root>
       EOF
 
+      @bar1 = @document.children[0].children[0].children[0]
       @baz1 = @document.children[0].children[0].children[1]
       @baz2 = @baz1.children[0]
       @baz3 = @document.children[0].children[1]
@@ -36,5 +37,10 @@ describe Oga::XPath::Evaluator do
       evaluate_xpath(@document, 'root/foo/bar/following::baz')
         .should == node_set(@baz1, @baz2, @baz3)
     end
+
+    example 'return a node set containing the siblings relative to root/foo/bar' do
+      evaluate_xpath(@bar1, 'following::baz')
+        .should == node_set(@baz1, @baz2, @baz3)
+    end
   end
 end

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

@@ -16,6 +16,7 @@ describe Oga::XPath::Evaluator do
 
       @foo1 = @document.children[0].children[0]
       @foo2 = @document.children[0].children[1].children[0]
+      @bar1 = @document.children[0].children[1]
     end
 
     example 'return a node set containing preceding siblings of root/bar' do
@@ -27,5 +28,9 @@ describe Oga::XPath::Evaluator do
       evaluate_xpath(@document, 'root/bar/baz/preceding-sibling::foo')
         .should == node_set(@foo2)
     end
+
+    example 'return a node set containing preceding siblings relative to root/bar' do
+      evaluate_xpath(@bar1, 'preceding-sibling::foo').should == node_set(@foo1)
+    end
   end
 end

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

@@ -19,6 +19,7 @@ describe Oga::XPath::Evaluator do
       @bar1 = @foo1.children[0]
       @baz1 = @foo1.children[1]
       @baz2 = @baz1.children[0]
+      @baz3 = @document.children[0].children[1]
     end
 
     example 'return a node set containing preceding nodes of root/foo/baz' do
@@ -30,5 +31,9 @@ describe Oga::XPath::Evaluator do
       evaluate_xpath(@document, 'root/baz/preceding::baz')
         .should == node_set(@baz1, @baz2)
     end
+
+    example 'return a node set containing preceding nodes relative to root/baz' do
+      evaluate_xpath(@baz3, 'preceding::baz').should == node_set(@baz1, @baz2)
+    end
   end
 end