Endure seeding test (#733)

Reported:
``` ruby
1) test_seeds :seed_a_school_with_lessons_and_students creates class with lessons for the owner
     Failure/Error: expect(Lesson.where(school_id:, school_class_id: school_class.id).length).to eq(2)

       expected: 2
            got: 4

       (compared using ==)
     # ./spec/lib/test_seeds_spec.rb:67:in 'block (3 levels) in <top (required)>'
     # ./spec/rails_helper.rb:108:in 'block (3 levels) in <top (required)>'
     # ./spec/rails_helper.rb:106:in 'block (2 levels) in <top (required)>'
```

Updated rake task to avoid duplicating Lesson.
Added a test to make sure idempotency on this rake task.

Diff seems bigger than it is, only small replacement.

Author: abcampo-iry

lib/tasks/test_seeds.rake

@@ -44,32 +44,31 @@ namespace :test_seeds do
 
   desc 'Create a school with lessons and students'
   task create: :environment do
-    if School.find_by(code: TEST_SCHOOL)
+    if School.exists?(id: TEST_SCHOOL)
       puts "Test school (#{TEST_SCHOOL}) already exists, run the destroy_seed_data task to start over)."
-      return
-    end
-
-    ActiveRecord::Base.transaction do
-      Rails.logger.info 'Attempting to seed data...'
-      creator_id = ENV.fetch('SEEDING_CREATOR_ID', TEST_USERS[:jane_doe])
-      teacher_id = ENV.fetch('SEEDING_TEACHER_ID', TEST_USERS[:john_doe])
+    else
+      ActiveRecord::Base.transaction do
+        Rails.logger.info 'Attempting to seed data...'
+        creator_id = ENV.fetch('SEEDING_CREATOR_ID', TEST_USERS[:jane_doe])
+        teacher_id = ENV.fetch('SEEDING_TEACHER_ID', TEST_USERS[:john_doe])
 
-      school = create_school(creator_id, TEST_SCHOOL)
-      verify_school(school)
-      assign_a_teacher(teacher_id, school)
+        school = create_school(creator_id, TEST_SCHOOL)
+        verify_school(school)
+        assign_a_teacher(teacher_id, school)
 
-      # for each of the owner and teacher, create a class and assign students
-      [creator_id, teacher_id].each do |user_id|
-        teacher_name = user_id == creator_id ? 'Jane Doe' : 'John Doe'
-        school_class = create_school_class(user_id, school, "#{teacher_name}'s Class", "A class for #{teacher_name}'s students")
-        assign_students(school_class, school)
+        # for each of the owner and teacher, create a class and assign students
+        [creator_id, teacher_id].each do |user_id|
+          teacher_name = user_id == creator_id ? 'Jane Doe' : 'John Doe'
+          school_class = create_school_class(user_id, school, "#{teacher_name}'s Class", "A class for #{teacher_name}'s students")
+          assign_students(school_class, school)
 
-        lessons = create_lessons(user_id, school, school_class)
-        lessons.each do |lesson|
-          create_project(user_id, school, lesson, 'print("Hello World!")')
+          lessons = create_lessons(user_id, school, school_class)
+          lessons.each do |lesson|
+            create_project(user_id, school, lesson, 'print("Hello World!")')
+          end
         end
+        Rails.logger.info 'Done...'
       end
-      Rails.logger.info 'Done...'
     end
   end
 end

spec/lib/test_seeds_spec.rb

@@ -84,6 +84,20 @@
       expect(ClassTeacher.where(teacher_id:).length).to eq(1)
     end
 
+    it 'is idempotent' do
+      school = School.find_by!(creator_id:)
+      owner_class = SchoolClass.joins(:teachers).find_by!(school_id: school.id, teachers: { teacher_id: creator_id })
+      teacher_class = SchoolClass.joins(:teachers).find_by!(school_id: school.id, teachers: { teacher_id: })
+
+      expect do
+        task.reenable
+        task.invoke
+      end.not_to change { [SchoolClass.where(school_id: school.id).count, Lesson.where(school_id: school.id).count, Project.where(school_id: school.id).count] }
+
+      expect(owner_class.reload.lessons.count).to eq(2)
+      expect(teacher_class.reload.lessons.count).to eq(2)
+    end
+
     it 'assigns students' do
       school_id = School.find_by(creator_id:).id
       school_class_id = SchoolClass.find_by(school_id:).id