Update include_relative tests

This verifies you can’t go “up” in the include

lib/jekyll/tags/include.rb

@@ -13,8 +13,6 @@ module Jekyll
 
     class IncludeTag < Liquid::Tag
 
-      SYNTAX_EXAMPLE = "{% include file.ext param='value' param2='value' %}"
-
       VALID_SYNTAX = /([\w-]+)\s*=\s*(?:"([^"\\]*(?:\\.[^"\\]*)*)"|'([^'\\]*(?:\\.[^'\\]*)*)'|([\w\.-]+))/
       VARIABLE_SYNTAX = /(?<variable>[^{]*\{\{\s*(?<name>[\w\-\.]+)\s*(\|.*)?\}\}[^\s}]*)(?<params>.*)/
 
@@ -30,6 +28,10 @@ module Jekyll
         validate_params if @params
       end
 
+      def syntax_example
+        "{% include file.ext param='value' param2='value' %}"
+      end
+
       def parse_params(context)
         params = {}
         markup = @params
@@ -59,7 +61,7 @@ Invalid syntax for include tag. File contains invalid characters or sequences:
 
 Valid syntax:
 
-  #{SYNTAX_EXAMPLE}
+  #{syntax_example}
 
 eos
         end
@@ -75,7 +77,7 @@ Invalid syntax for include tag:
 
 Valid syntax:
 
-  #{SYNTAX_EXAMPLE}
+  #{syntax_example}
 
 eos
         end
@@ -154,6 +156,10 @@ eos
         page_path = context.registers[:page].nil? ? includes_dir : File.dirname(context.registers[:page]["path"])
         Jekyll.sanitized_path(context.registers[:site].source, page_path)
       end
+
+      def syntax_example
+        "{% include_relative file.ext param='value' param2='value' %}"
+      end
     end
   end
 end

test/test_tags.rb

@@ -568,6 +568,25 @@ CONTENT
           assert_equal 'Included file \'./missing.html\' not found', exception.message
         end
       end
+
+      context "include existing file above you" do
+        setup do
+          @content = <<CONTENT
+---
+title: higher file
+---
+
+{% include_relative ../README.markdown %}
+CONTENT
+        end
+
+        should "raise error relative to source directory" do
+          exception = assert_raise ArgumentError do
+            create_post(@content, {'permalink' => 'pretty', 'source' => source_dir, 'destination' => dest_dir, 'read_posts' => true})
+          end
+          assert_equal "Invalid syntax for include tag. File contains invalid characters or sequences:\n\n  ../README.markdown\n\nValid syntax:\n\n  {% include_relative file.ext param='value' param2='value' %}\n\n", exception.message
+        end
+      end
     end
 
     context "with symlink'd include" do