Add a predicate method to each node

This allows the AST to be searched via a predicate method rather than
hardcoding the class name and doing is_a? checks.  For example, rather
than:

```
ast.grep(Psych::Nodes::Scalar).each do |node|
  # .. do something
end
```

Now you can do:

```
ast.find_all(&:scalar?).each do |node|
  # .. do something
end
```

Your code no longer needs to know the exact class used in the AST.

1 files changed, 16 insertions, 0 deletions

diff --git a/test/psych/test_stream.rb b/test/psych/test_stream.rb
index 3bd557c..9b71c6d 100644
--- a/test/psych/test_stream.rb
+++ b/test/psych/test_stream.rb
@@ -3,6 +3,22 @@ require_relative 'helper'
 
 module Psych
   class TestStream < TestCase
+    [
+      [Psych::Nodes::Alias, :alias?],
+      [Psych::Nodes::Document, :document?],
+      [Psych::Nodes::Mapping, :mapping?],
+      [Psych::Nodes::Scalar, :scalar?],
+      [Psych::Nodes::Sequence, :sequence?],
+      [Psych::Nodes::Stream, :stream?],
+    ].each do |klass, block|
+      define_method :"test_predicate_#{block}" do
+        rb = Psych.parse_stream("---\n- foo: bar\n- &a !!str Anchored\n- *a")
+        nodes = rb.grep(klass)
+        assert_operator nodes.length, :>, 0
+        assert_equal nodes, rb.find_all(&block)
+      end
+    end
+
     def test_parse_partial
       rb = Psych.parse("--- foo\n...\n--- `").to_ruby
       assert_equal 'foo', rb