How to enable Rails' file_fixture helper in FactoryBot

In FactoryBot factories, Rails' file_fixture is not available by default. To enable it, include a support module from rspec-rails:

FactoryBot::SyntaxRunner.include(RSpec::Rails::FileFixtureSupport)

That includes ActiveSupport::Testing::FileFixtures, where file_fixture is defined, but also configures the file_fixture_path so that you can actually use file_fixture.