add test coverage for unlinking orphan nodes

fixes #1112
closes #1152

CHANGELOG.rdoc

@@ -24,6 +24,7 @@ Several changes were made to improve performance:
 * [JRuby] fix NPE when inspecting nodes returned by NodeSet#drop (#1042) (Thanks, @mkristian!)
 * [JRuby] fix nil attriubte node's namespace in reader (#1327) (Thanks, @codekitchen!)
 * [JRuby] fix Nokogiri munging unicode characters that require more than 2 bytes (#1113) (Thanks, @mkristian!)
+* [JRuby] allow unlinking an unparented node (#1112, #1152) (Thanks, @esse!)
 * [MRI] fix assertion failure while accessing attribute node's namespace in reader (#843) (Thanks, @2potatocakes!)
 * [MRI] fix issue with GCing namespace nodes returned in an xpath query. (#1155)
 * [MRI] Ensure C strings are null-terminated. (#1381)

ext/java/nokogiri/XmlNode.java

@@ -1413,16 +1413,10 @@ public IRubyObject set_namespace(ThreadContext context, IRubyObject namespace) {
 
     @JRubyMethod(name = {"unlink", "remove"})
     public IRubyObject unlink(ThreadContext context) {
-        if(node.getParentNode() == null) {
-            //throw context.getRuntime().newRuntimeError("TYPE: " + node.getNodeType()+ " PARENT NULL");
-            return this;
-            // if node doesn't have parent node - simply return self, as would Nokogiri for C would do
-            // because that means that node is already detached
-        } else {
+        if (node.getParentNode() != null) {
             clearXpathContext(node.getParentNode());
             node.getParentNode().removeChild(node);
         }
-
         return this;
     }
 

test/html/test_document_fragment.rb

@@ -23,7 +23,8 @@ def test_html_parse_encoding
       end
 
       def test_unlink_empty_document
-        Nokogiri::HTML::DocumentFragment.parse('').unlink
+        frag = Nokogiri::HTML::DocumentFragment.parse('').unlink # must_not_raise
+        assert_nil frag.parent
       end
 
       def test_colons_are_not_removed

test/xml/test_unparented_node.rb

@@ -422,6 +422,19 @@ def test_illegal_replace_of_node_with_doc
         old_node = @node.at('.//employee')
         assert_raises(ArgumentError){ old_node.replace new_node }
       end
+
+      def test_unlink_on_unlinked_node_1
+        node = Nokogiri::XML::Node.new 'div', Nokogiri::XML::Document.new
+        node.unlink # must_not_raise
+        assert_nil node.parent
+      end
+
+      def test_unlink_on_unlinked_node_2
+        node = Nokogiri::XML('<div>foo</div>').at_css("div")
+        node.unlink
+        node.unlink # must_not_raise
+        assert_nil node.parent
+      end
     end
   end
 end