Add an instance method to check the relationship between 2 nodes

Author: rnitta

README.md

@@ -369,6 +369,7 @@ When you include ```has_closure_tree``` in your model, you can provide a hash to
 * ```tag.descendant_of?(node)``` returns true if current node is descendant of another one
 * ```tag.self_and_descendants``` returns a scope of self, all children, childrens' children, etc., ordered by depth.
 * ```tag.self_and_descendant_ids``` returns IDs of self, all children, childrens' children, etc., ordered by depth.
+* ```tag.family_of?``` returns true if current node and another one have a same root.
 * ```tag.hash_tree``` returns an [ordered, nested hash](#nested-hashes) that can be depth-limited.
 * ```tag.find_by_path(path)``` returns the node whose name path *from ```tag```* is ```path```. See (#find_or_create_by_path).
 * ```tag.find_or_create_by_path(path)``` returns the node whose name path *from ```tag```* is ```path```, and will create the node if it doesn't exist already.See (#find_or_create_by_path).

lib/closure_tree/model.rb

@@ -159,6 +159,11 @@ def child_of?(node)
       self.parent == node
     end
 
+    # node and record have a same root
+    def family_of?(node)
+      self.root == node.root
+    end
+
     # Alias for appending to the children collection.
     # You can also add directly to the children collection, if you'd prefer.
     def add_child(child_node)

spec/label_spec.rb

@@ -633,6 +633,14 @@ def roots_name_and_order
       expect(@d2.descendant_of?(@a1)).to be_truthy
       expect(@b1.descendant_of?(@a2)).to be_falsey      
     end
+
+    it "checks descendant of node" do
+      expect(@b1.family_of?(@b1)).to be_truthy
+      expect(@a1.family_of?(@c1)).to be_truthy
+      expect(@d3.family_of?(@a2)).to be_truthy
+      expect(@c1.family_of?(@d2)).to be_truthy
+      expect(@c3.family_of?(@a1)).to be_falsey
+    end
   end
 
 end