Add ExcerptDrop and remove excerpt's ability to refer to itself in Liquid

test/test_excerpt_drop.rb

@@ -0,0 +1,31 @@
+require 'helper'
+
+class TestExcerptDrop < JekyllUnitTest
+  context "an excerpt drop" do
+    setup do
+      @site = fixture_site
+      @site.read
+      @doc = @site.docs_to_write.first
+      @doc_drop = @doc.to_liquid
+      @excerpt = @doc.data['excerpt']
+      @excerpt_drop = @excerpt.to_liquid
+    end
+
+    should "have the right thing" do
+      assert @doc.is_a? Jekyll::Document
+      assert @doc_drop.is_a? Jekyll::Drops::DocumentDrop
+      assert @excerpt.is_a? Jekyll::Excerpt
+      assert @excerpt_drop.is_a? Jekyll::Drops::ExcerptDrop
+    end
+
+    should "not have an excerpt" do
+      assert_nil @excerpt.data['excerpt']
+      assert @excerpt_drop.class.invokable? 'excerpt'
+      assert_nil @excerpt_drop['excerpt']
+    end
+
+    should "inherit values from the document" do
+      assert_equal @excerpt_drop.keys, @doc_drop.keys
+    end
+  end
+end