Tweak test formatting; fix order-dependent failure

The order-dependent failure has been been commented in code.

After manually bisecting the test suite, I was able to determine that
the template cascade tests were leaving the `@@template_priority_path`
set to an overridden value in tests run afterward.

lib/gollum/views/template_cascade.rb

@@ -11,9 +11,13 @@ module Precious
       end
 
       def first_path_available(name)
-        priority = File.join(template_priority_path, "#{name}.#{template_extension}")
         default = File.join(template_path, "#{name}.#{template_extension}")
-        File.exists?(priority) ? priority : default
+        priority =
+          if template_priority_path
+            File.join(template_priority_path, "#{name}.#{template_extension}")
+          end
+
+        priority && File.exists?(priority) ? priority : default
       end
 
       # Method should track lib/mustache/settings.rb from Mustache project.

test/test_template_cascade.rb

@@ -1,47 +1,59 @@
 # ~*~ encoding: utf-8 ~*~
 require File.expand_path(File.join(File.dirname(__FILE__), 'helper'))
 
-class TestTemplateCascade < Minitest::Unit::TestCase
+context "Precious::Views::TemplateCascade" do
   include Rack::Test::Methods
 
-  def setup
+  setup do
     @path = cloned_testpath('examples/lotr.git')
     Precious::App.set(:gollum_path, @path)
-    Precious::App.set(:wiki_options, {template_dir: testpath('examples/template_cascade')})
+    Precious::App.set(
+      :wiki_options,
+      {template_dir: testpath('examples/template_cascade')}
+    )
     @wiki = Gollum::Wiki.new(@path)
   end
 
-  def teardown
+  teardown do
     FileUtils.rm_rf(@path)
+
+    Precious::App.set(:wiki_options, {template_dir: nil})
+
+    # The following line has been added to avoid order-dependent test failures.
+    # We saw issues where the class variable `@@template_priority_path` was not
+    # being reset between test cases.
+    Precious::Views::TemplateCascade.class_variable_set(
+      :@@template_priority_path,
+      nil
+    )
   end
 
   def app
-    Precious::App
+    Precious::App.new
   end
 
-  def test_overridden_page_template_is_used
+  test "overridden_page_template_is_used" do
     get '/Home'
 
     assert last_response.body.include?('PAGE_OVERRIDE')
   end
 
-  def test_overridden_navbar_partial_is_used
+  test "test_overridden_navbar_partial_is_used" do
     get '/Home'
 
     assert last_response.body.include?('NAVBAR_OVERRIDE')
   end
 
-  def test_overridden_templates_are_ignore_without_template_dir_set
+  test "test_overridden_templates_are_ignore_without_template_dir_set" do
     Precious::App.set(:wiki_options, {template_dir: nil})
 
     get '/Home'
+
     assert_equal '/Home', last_request.fullpath
+
     assert last_response.ok?
+
     refute_match /PAGE_OVERRIDE/, last_response.body
     refute_match /NAVBAR_OVERRIDE/, last_response.body
   end
-
-  def teardown
-    FileUtils.rm_rf(@path)
-  end
 end