Add test for asset_hashing rack-filtered items.

middleman-more/features/asset_hash.feature

@@ -85,3 +85,17 @@ Feature: Assets get a file hash appended to their and references to them are upd
       """
     When I go to "/partials/"
     Then I should see 'href="../stylesheets/uses_partials-e8c3d4eb.css'
+
+  Scenario: The asset hash should change when a Rack-based filter changes
+    Given a fixture app "asset-hash-app"
+    And a file named "config.rb" with:
+      """
+      activate :asset_hash
+      activate :relative_assets
+      activate :directory_indexes
+      require 'lib/middleware.rb'
+      use Middleware
+      """
+    Given the Server is running at "asset-hash-app"
+    When I go to "/"
+    Then I should see 'href="stylesheets/site-5770af52.css'

middleman-more/fixtures/asset-hash-app/lib/middleware.rb

@@ -0,0 +1,16 @@
+class Middleware
+  def initialize(app)
+    @app = app
+  end
+
+  def call(env)
+    status, headers, response = @app.call(env)
+    body = ''
+    response.each {|part| body += part }
+    if (env["PATH_INFO"] =~ /css$/)
+      body += "\n/* Added by Rack filter */"
+      status, headers, response = Rack::Response.new(body, status, headers).finish
+    end
+    [status, headers, response]
+  end
+end