How to isolate fixtures to specific Rails tests

Question

How can I isolate the usage of fixtures to specific tests?

In my setup some of my tests rely on fixture data and some don't, so the default of loading all my fixtures in test_helper.rb with fixtures :all breaks my tests.

Example integration test that requires empty behaviorists table:

require 'test_helper'

class WelcomeFlowTest < ActionDispatch::IntegrationTest
  test "when no user is found start welcome flow" do
    get "/"
    follow_redirect!
    assert_response :success

    post "/setup", {
      behaviorist: { name: "Andy", email: "[email protected]" },
      habit: { name: "Interval running", on_monday: false, on_tuesday: true, \
               on_wednesday: false, on_thursday: true, on_friday: false, \
               on_saturday: true, on_sunday: false }
    }
    assert_response :success
    assert_equal 1, Behaviorist.count
    assert_equal 1, Habit.count
  end
end

My unit test that requires behaviorist fixtures:

require 'test_helper'

class BehavioristTest < ActiveSupport::TestCase
  test "validates uniqueness of :name" do
    andy = Behaviorist.new(name: "Andy", remote_ip: "127.0.0.1")
    assert_not run.valid?
    assert_match /has already been taken/, andy.errors[:name].join
  end
end

Answer 1

With a little digging on how Rails implements fixtures I see that fixtures, once loaded, are isolated from changes within each TestCase via a transaction. My working solution is to remove loading the fixtures :all inside the test_helper.rb. Then for each test that requires fixtures I override the default of using transactional fixtures, load specific fixtures, and then remove them on teardown.

Example of isolated fixtures for single TestCase:

require 'test_helper'

class BehavioristTest < ActiveSupport::TestCase
  self.use_transactional_fixtures = false
  fixtures :behaviorists
  teardown :delete_behaviorists

  test "validates uniqueness of :name" do
    andy = Behaviorist.new(name: "Andy", remote_ip: "127.0.0.1")
    assert_not run.valid?
    assert_match /has already been taken/, run.errors[:name].join
  end

  private

  def delete_behaviorists
    Behaviorist.delete_all
  end
end