add tests for controllers and ActionCable channels; improve main backend docs

main-server/app/controllers/api/sessions_controller.rb

@@ -2,7 +2,9 @@ class Api::SessionsController < ApplicationController
   skip_before_action :authenticate_request!, only: [:create]
 
   def create
-    user = User.authenticate_by(params.permit(:nickname, :password))
+    user = if params[:nickname].present? && params[:password].present?
+      User.authenticate_by(params.permit(:nickname, :password))
+    end
 
     if user
       token = JwtService.encode(user_id: user.id)

main-server/app/jobs/application_job.rb

@@ -0,0 +1,7 @@
+class ApplicationJob < ActiveJob::Base
+  # Automatically retry jobs that encountered a deadlock
+  # retry_on ActiveRecord::Deadlocked
+
+  # Most jobs are safe to ignore if the underlying records are no longer available
+  # discard_on ActiveJob::DeserializationError
+end