Specs for various XPath evaluator helper methods.

lib/oga/xpath/evaluator.rb

@@ -1219,6 +1219,17 @@ module Oga
         return node
       end
 
+      ##
+      # Returns the text of the first node in the node set, or an empty string
+      # if the node set is empty.
+      #
+      # @param [Oga::XML::NodeSet] set
+      # @return [String]
+      #
+      def first_node_text(set)
+        return set[0].respond_to?(:text) ? set[0].text : ''
+      end
+
       ##
       # Returns a node set containing all the child nodes of the given set of
       # nodes.

spec/oga/xpath/evaluator/general_spec.rb

@@ -6,6 +6,46 @@ describe Oga::XPath::Evaluator do
     @evaluator = described_class.new(@document)
   end
 
+  context '#function_node' do
+    before do
+      @context_set = Oga::XML::NodeSet.new([@document])
+    end
+
+    example 'return the first node in the expression' do
+      exp  = s(:axis, 'child', s(:test, nil, 'a'))
+      node = @evaluator.function_node(@context_set, exp)
+
+      node.should == @document.children[0]
+    end
+
+    example 'raise a TypeError if the expression did not return a node set' do
+      exp   = s(:call, 'false')
+      block = lambda { @evaluator.function_node(@context_set, exp) }
+
+      block.should raise_error(TypeError)
+    end
+
+    example 'use the current context node if the expression is empty' do
+      a_node = @document.children[0]
+
+      @evaluator.stub(:current_node).and_return(a_node)
+
+      @evaluator.function_node(@context_set).should == a_node
+    end
+  end
+
+  context '#first_node_text' do
+    example 'return the text of the first node' do
+      @evaluator.first_node_text(@document.children).should == 'Hello'
+    end
+
+    example 'return an empty string if the node set is empty' do
+      set = Oga::XML::NodeSet.new
+
+      @evaluator.first_node_text(set).should == ''
+    end
+  end
+
   context '#child_nodes' do
     before do
       @children = Oga::XML::NodeSet.new([