Introduce rspec helper to improve performance ⚡️

Use `shared_association_default` to create default values to be used for
factory associations in rspec. They get created only once.

For instance, when creating work packages with `create(:work_package)`,
a new user gets created for each create work package. To reuse the same
user for all created work packages, add this in your example group:

    shared_association_default(:user) { create(:user) }

spec/services/work_packages/schedule_dependency/dependency_spec.rb

@@ -36,9 +36,9 @@ require 'rails_helper'
 RSpec.describe WorkPackages::ScheduleDependency::Dependency do
   subject(:dependency) { dependency_for(work_package_used_in_dependency) }
 
-  shared_let(:author) { create(:user, firstname: 'Dummy user to reduce number of created users') }
-  shared_let(:project) { create(:project_with_types, name: 'Dummy project to reduce number of created projects') }
-  shared_let(:work_package) { create(:work_package, subject: 'moved', author:, project:) }
+  create_shared_association_defaults_for_work_package_factory
+
+  shared_let(:work_package) { create(:work_package, subject: 'moved') }
 
   let(:schedule_dependency) { WorkPackages::ScheduleDependency.new(work_package) }
 
@@ -54,25 +54,25 @@ RSpec.describe WorkPackages::ScheduleDependency::Dependency do
   end
 
   def create_predecessor_of(work_package, **attributes)
-    create(:work_package, subject: "predecessor of #{work_package.subject}", author:, project:, **attributes).tap do |predecessor|
+    create(:work_package, subject: "predecessor of #{work_package.subject}", **attributes).tap do |predecessor|
       create(:follows_relation, from: work_package, to: predecessor)
     end
   end
 
   def create_follower_of(work_package)
-    create(:work_package, subject: "follower of #{work_package.subject}", author:, project:).tap do |follower|
+    create(:work_package, subject: "follower of #{work_package.subject}").tap do |follower|
       create(:follows_relation, from: follower, to: work_package)
     end
   end
 
   def create_parent_of(work_package)
-    create(:work_package, subject: "parent of #{work_package.subject}", author:, project:).tap do |parent|
+    create(:work_package, subject: "parent of #{work_package.subject}").tap do |parent|
       work_package.update(parent:)
     end
   end
 
   def create_child_of(work_package)
-    create(:work_package, subject: "child of #{work_package.subject}", author:, project:, parent: work_package)
+    create(:work_package, subject: "child of #{work_package.subject}", parent: work_package)
   end
 
   describe '#dependent_ids' do

spec/services/work_packages/set_schedule_service_spec.rb

@@ -29,14 +29,11 @@
 require 'spec_helper'
 
 describe WorkPackages::SetScheduleService do
-  shared_let(:project) { create(:project) }
-  shared_let(:user) { create(:user) }
-  shared_let(:type) { create(:type) }
+  create_shared_association_defaults_for_work_package_factory
 
   let(:work_package) do
     create(:work_package,
            subject: 'subject',
-           project:,
            start_date: work_package_start_date,
            due_date: work_package_due_date)
   end
@@ -98,12 +95,9 @@ describe WorkPackages::SetScheduleService do
   def create_follower(start_date, due_date, predecessors, parent: nil)
     work_package = create(:work_package,
                           subject: "follower of #{predecessors.keys.map(&:subject).to_sentence}",
-                          type:,
                           start_date:,
                           due_date:,
-                          parent:,
-                          project:,
-                          author: user)
+                          parent:)
 
     predecessors.map do |predecessor, delay|
       create(:follows_relation,
@@ -311,7 +305,6 @@ describe WorkPackages::SetScheduleService do
     context 'when moving backwards with the follower having another relation limiting movement' do
       let!(:other_work_package) do
         create(:work_package,
-               type:,
                start_date: follower1_start_date - 8.days,
                due_date: follower1_start_date - 5.days).tap do |wp|
           create(:follows_relation,
@@ -627,9 +620,6 @@ describe WorkPackages::SetScheduleService do
     context 'when moving backwards with the parent having another relation limiting movement' do
       let!(:other_work_package) do
         create(:work_package,
-               type:,
-               project:,
-               author: user,
                start_date: Time.zone.today - 8.days,
                due_date: Time.zone.today - 4.days).tap do |wp|
           create(:follows_relation,
@@ -654,7 +644,6 @@ describe WorkPackages::SetScheduleService do
     context 'when moving backwards with the parent having another relation not limiting movement' do
       let(:other_work_package) do
         create(:work_package,
-               type:,
                start_date: Time.zone.today - 10.days,
                due_date: Time.zone.today - 9.days)
       end

spec/support/shared_let.rb

@@ -33,7 +33,7 @@
 # and the creation is rolled back in an after_all hook.
 #
 # Caveats: Set +reload: true+ if you plan to modify this value, otherwise Rails may still
-# have cached the local value. This will perform a database update, but is much faster
+# have cached the local value. This will perform a database select, but is much faster
 # than creating new records (especially, work packages).
 #
 # Since test-prof added `let_it_be` this is only a wrapper for it
@@ -41,3 +41,33 @@
 def shared_let(key, reload: true, refind: false, &block)
   let_it_be(key, reload:, refind:, &block)
 end
+
+# Defines an object to be used by default for all FactoryBot association
+# matching they key name.
+#
+# The object is created only once in the example group, and reused for each
+# example. Under the hood, it uses +let_it_be+ and +FactoryDefault+ from the
+# test_prof gem.
+#
+# For instance, when creating work packages with +create(:work_package)+, a new
+# user gets created for each create work package. To reuse the same user for all
+# created work packages, in your example group add:
+#
+#   shared_association_default(:user) { create(:user) }
+#
+def shared_association_default(key, factory_name: key, &block)
+  # unique let identifier to prevent clashes
+  let_it_be(key, reload: true, &block)
+
+  before do
+    set_factory_default(factory_name, send(key))
+  end
+end
+
+# Use this to boost performance in tests creating lots of work packages.
+def create_shared_association_defaults_for_work_package_factory
+  shared_association_default(:priority) { create(:priority) }
+  shared_association_default(:project_with_types) { create(:project_with_types) }
+  shared_association_default(:status) { create(:status) }
+  shared_association_default(:user) { create(:user) }
+end