This is test/test_helper.rb after creating a new Rails 7 app with Minitest:

ENV["RAILS_ENV"] ||= "test"
require_relative "../config/environment"
require "rails/test_help"

class ActiveSupport::TestCase
  # Run tests in parallel with specified workers
  parallelize(workers: :number_of_processors)

  # Setup all fixtures in test/fixtures/*.yml for all tests in alphabetical order.
  fixtures :all

  # Add more helper methods to be used by all tests here...

fixtures: all will load all fixtures once before the test cases. I think this is the only reasonable way to use fixtures.

If you want to achieve this with RSpec then you need to add the following to spec/rails_helper.rb:

config.global_fixtures = :all

It may seem to make sense to load fixtures within an example group:

describe Thing do
  fixtures :thing

  it 'checks something' do
    expect(things(:one).name).to eq 'First'

The problem with this approach is that fixtures will be loaded before the transaction of the example starts so they won’t be rolled back. This means that the created records will be leaked to the next example group. This is probably not what you want.