Validate options type for TreeNode (#45)

Raise ArgumentError when a non-hash options value is provided to
Tree::TreeNode.new, and add coverage in the core test suite.

Author: evolve75

lib/tree.rb

@@ -271,7 +271,9 @@ def validate_acyclic!
     #
     # @see #[]
     def initialize(name, content = nil, options = nil)
-      options = {} unless options.is_a?(Hash)
+      raise ArgumentError, 'Options must be a hash' if options && !options.is_a?(Hash)
+
+      options ||= {}
       @checks_enabled = options.fetch(:checks, true)
 
       raise ArgumentError, 'Node name HAS to be provided!' if checks_enabled? && name.nil?

test/test_tree.rb

@@ -80,6 +80,7 @@ def test_root_setup
       assert_equal(0, @root.in_degree, 'Root should have an in-degree of 0')
       assert_equal(0, @root.node_height, "Root's height before adding any children is 0")
       assert_raise(ArgumentError) { Tree::TreeNode.new(nil) }
+      assert_raise(ArgumentError) { Tree::TreeNode.new('ROOT', nil, :bad) }
     end
 
     def test_root