Test #141

This isn't ideal, we're directly inspecting the cache, but I don't know how to cause a second asset to actually use the information in the cache to incorrectly load an asset. If someone could show me how, that would be great and I'll update the test. To understand the failure mode see: #141 (comment)

test/test_caching.rb

@@ -393,6 +393,41 @@ def teardown
     assert !asset1.equal?(asset2)
   end
 
+  test "history cache is not polluted" do
+    dependency_file = File.join(fixture_path('asset'), "dependencies", "a.js")
+    env1 = Sprockets::Environment.new(fixture_path('asset')) do |env|
+      env.append_path(".")
+      env.cache = @cache
+    end
+    env1['required_assets.js']
+
+    sandbox dependency_file do
+      write(dependency_file, "var aa = 2;")
+      env1['required_assets.js']
+
+      # We must use private APIs to test this behavior
+      # https://github.com/rails/sprockets/pull/141
+      cache_entries = @cache.send(:find_caches).map do |file, _|
+        key    = file.gsub(/\.cache\z/, ''.freeze).split(@cache_dir).last
+        result = @cache.get(key)
+
+        if result.is_a?(Array)
+          result if result.first.is_a?(Set)
+        else
+          nil
+        end
+      end.compact
+
+      assert cache_entries.any?
+
+      cache_entries.each do |sets|
+        sets.each do |set|
+          refute set.any? {|uri| uri.include?(env1.root) }, "Expected entry in cache to not include absolute paths but did: #{set.inspect}"
+        end
+      end
+    end
+  end
+
   test "no absolute paths are retuned from cache" do
     env1 = Sprockets::Environment.new(fixture_path('default')) do |env|
       env.append_path(".")