Fix #507

Rakefile

@@ -117,7 +117,7 @@ task :gemspec => :validate do
     split("\n").
     sort.
     reject { |file| file =~ /^\./ }.
-    reject { |file| file =~ /^(rdoc|pkg)/ }.
+    reject { |file| file =~ /^(rdoc|pkg|test)/ }.
     map { |file| "    #{file}" }.
     join("\n")
 
@@ -139,4 +139,4 @@ task :validate do
     puts "A `VERSION` file at root level violates Gem best practices."
     exit!
   end
-end
+end