Add rake task to run tests from host app

saas/lib/tasks/fizzy/saas_tasks.rake

@@ -1,4 +1,16 @@
-# desc "Explaining what the task does"
-# task :fizzy_saas do
-#   # Task goes here
-# end
+require "rake/testtask"
+
+namespace :test do
+  desc "Run tests for fizzy-saas gem"
+  Rake::TestTask.new(:saas) do |t|
+    t.libs << "test"
+    t.test_files = FileList[Fizzy::Saas::Engine.root.join("test/**/*_test.rb")]
+    t.verbose = true
+  end
+end
+
+task "test:saas" => :environment do
+  $LOAD_PATH.unshift Fizzy::Saas::Engine.root.join("test").to_s
+
+  require "test_helper"
+end