[ci] Add rspec test for project watchlist

* Migrate project watchlist tests to rspec test suite
* Fix caching issue that appears when changing watched projects within a second,
  first found in 82e3407...

src/api/app/models/user.rb

@@ -916,19 +916,25 @@ def self.realname_for_login(person)
   end
 
   def watched_project_names
-    @watched_projects ||= Rails.cache.fetch(['watched_project_names', self]) do
+    Rails.cache.fetch(['watched_project_names', self]) do
       Project.where(id: watched_projects.pluck(:project_id)).pluck(:name).sort
     end
   end
 
   def add_watched_project(name)
     watched_projects.create(project: Project.find_by_name!(name))
-    self.touch
+    clear_watched_projects_cache
   end
 
   def remove_watched_project(name)
     watched_projects.joins(:project).where(projects: { name: name }).delete_all
-    self.touch
+    clear_watched_projects_cache
+  end
+
+  # Needed to clear cache even when user's updated_at timestamp did not change,
+  # aka. changes within the same second. Mainly an issue when in our test suite
+  def clear_watched_projects_cache
+    Rails.cache.delete(['watched_project_names', self])
   end
 
   def watches?(name)