TDD Fundamental cleanup exercise

Testing
1

I’m trying to refactor and do a cleanup exercise from this repo and this is my solution:

RSpec.describe Invitation do
  # this is the helper
  def create_user_and_build_invitation
    team_owner = User.create 
    team = Team.create name: "A fine team", owner: team_owner
    team_owner.update team: team
    new_user = User.create(email: 'rookie@example.com')

    [new_user, Invitation.new(team: team, user: new_user)]
  end
  
  # some lines below are deleted
  describe "callbacks" do
    describe "after_save" do
      context "with valid data" do
        it "invites the user" do
          new_user, invitation = create_user_and_build_invitation
          invitation.save
          expect(new_user).to be_invited
        end
      end

      context "with invalid data" do
        it "does not save the invitation" do
          new_user, invitation = create_user_and_build_invitation
          invitation.team = nil
          invitation.save

          expect(invitation).not_to be_valid
          expect(invitation).to be_new_record
        end

        # ...
      end
    end
  end

  describe "#event_log_statement" do
    context "when the record is saved" do
      it "include the name of the team" do
        new_user, invitation = create_user_and_build_invitation
        invitation.save
        log_statement = invitation.event_log_statement
        expect(log_statement).to include("A fine team")
      end

      # ...
    end

    context "when the record is not saved but valid" do
      it "includes the name of the team" do
        new_user, invitation = create_user_and_build_invitation
        log_statement = invitation.event_log_statement
        expect(log_statement).to include("A fine team")
      end

      # ...
    end

    context "when the record is not saved and not valid" do
      it "includes INVALID" do
        new_user, invitation = create_user_and_build_invitation
        invitation.user = nil
        log_statement = invitation.event_log_statement
        expect(log_statement).to include("INVALID")
      end
    end
  end
end

and I have some questions:

  1. Do you have any advice to improve the code above?
  2. Do I need to split the helper into two: one for generating the invitation and the second for generating the new_user?
  3. Why this cleanup can decrease test running time? I mean the helper is creating some variable and called in each test anyway so I don’t feel like this brings more performance to the test (as far as I know, and I am new to rspec and TDD)
    Thanks for your time and assistance. I truly appreciate your help and insights.