Add type attribute to Document instances (#7406)

Merge pull request 7406

test/test_document.rb

@@ -58,6 +58,10 @@ class TestDocument < JekyllUnitTest
       assert_equal "configuration", @document.basename_without_ext
     end
 
+    should "know its type" do
+      assert_equal :methods, @document.type
+    end
+
     should "know whether it's a YAML file" do
       assert_equal false, @document.yaml_file?
     end

test/test_excerpt.rb

@@ -56,6 +56,15 @@ class TestExcerpt < JekyllUnitTest
       end
     end
 
+    context "#type" do
+      should "return the post's type" do
+        assert_equal @excerpt.type, @post.type
+      end
+      should "return a symbol" do
+        assert_same @excerpt.type.class, Symbol
+      end
+    end
+
     context "#to_s" do
       should "return rendered output" do
         assert_equal @excerpt.output, @excerpt.to_s