Added various predicate specs for XPath axes.

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

@@ -22,6 +22,10 @@ describe Oga::XPath::Evaluator do
       evaluate_xpath(@c1, 'ancestor-or-self::c').should == node_set(@c1)
     end
 
+    example 'return a node set containing the first ancestor' do
+      evaluate_xpath(@c1, 'ancestor-or-self::*[1]').should == node_set(@c1)
+    end
+
     example 'return an empty node set for non existing ancestors' do
       evaluate_xpath(@c1, 'ancestor-or-self::foo').should == node_set
     end

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

@@ -18,6 +18,10 @@ describe Oga::XPath::Evaluator do
       evaluate_xpath(@c1, 'ancestor::a').should == node_set(@a1)
     end
 
+    example 'return a node set containing the first ancestor' do
+      evaluate_xpath(@c1, 'ancestor::*[1]').should == node_set(@b1)
+    end
+
     example 'return an empty node set for non existing ancestors' do
       evaluate_xpath(@c1, 'ancestor::c').should == node_set
     end

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

@@ -45,6 +45,11 @@ describe Oga::XPath::Evaluator do
         .should == node_set(@c1)
     end
 
+    example 'return a node set containing the first descendant' do
+      evaluate_xpath(@document, 'descendant-or-self::b[1]')
+        .should == node_set(@b1)
+    end
+
     example 'return an empty node set for a non existing descendant' do
       evaluate_xpath(@document, 'descendant-or-self::foobar').should == node_set
     end

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

@@ -22,6 +22,10 @@ describe Oga::XPath::Evaluator do
       evaluate_xpath(@document, 'a/descendant::a').should == node_set(@a2)
     end
 
+    example 'return a node set containing the first descendant' do
+      evaluate_xpath(@document, 'descendant::a[1]').should == node_set(@a1)
+    end
+
     example 'return an empty node set for non existing descendants' do
       evaluate_xpath(@document, 'a/b/c/descendant::c').should == node_set
     end