Update the Rakefile setup

Backport a few tricks from solidus_dev_support and fix `rake clobber`
which was called by bin/setup, but broken.

Keep supporting the old task names as deprecated.

Rakefile

@@ -3,21 +3,38 @@
 require 'bundler'
 Bundler::GemHelper.install_tasks
 
-require 'rspec/core/rake_task'
+require 'rake/clean'
 require 'spree/testing_support/common_rake'
+ENV['DUMMY_PATH'] = "spec/dummy"
+ENV['LIB_NAME'] = "solidus/auth"
+::CLOBBER.include ENV['DUMMY_PATH']
 
-RSpec::Core::RakeTask.new
+namespace :extension do
+  # We need to go back to the gem root since the upstream
+  # extension:test_app changes the working directory to be the dummy app.
+  task :test_app do
+    Rake::Task['extension:test_app'].invoke
+    cd __dir__
+  end
 
-task :default do
-  if Dir["spec/dummy"].empty?
-    Rake::Task[:test_app].invoke
-    Dir.chdir("../../")
+  directory ENV['DUMMY_PATH'] do
+    Rake::Task['common:test_app'].invoke("Spree::User")
   end
-  Rake::Task[:spec].invoke
-end
 
-desc 'Generates a dummy app for testing'
-task :test_app do
-  ENV['LIB_NAME'] = 'solidus/auth'
-  Rake::Task['common:test_app'].invoke("Spree::User")
+  require 'rspec/core/rake_task'
+  RSpec::Core::RakeTask.new(:specs, [] => FileList[ENV['DUMMY_PATH']]) do |t|
+    # Ref: https://circleci.com/docs/2.0/configuration-reference#store_test_results
+    # Ref: https://github.com/solidusio/circleci-orbs-extensions#test-results-rspec
+    if ENV['TEST_RESULTS_PATH']
+      t.rspec_opts =
+        "--format progress " \
+        "--format RspecJunitFormatter --out #{ENV['TEST_RESULTS_PATH']}"
+    end
+  end
 end
+
+task default: 'extension:specs'
+
+# DEPRECATED:
+task test_app: 'extension:test_app'
+task spec: 'extension:specs'