Timestamp columns are not auto populated for hm:t join tables

_hmt_fixture_bug.rb

ENV['FIXTURES_DIR'] = "./"

begin
  require 'bundler/inline'
rescue LoadError => e
  $stderr.puts 'Bundler version 1.10 or later is required. Please update your Bundler'
  raise e
end

gemfile(true) do
  source 'https://rubygems.org'
  gem 'rails', github: 'rails/rails'
  gem 'arel', github: 'rails/arel'
  gem 'rack', github: 'rack/rack'
  gem 'sqlite3'
end

require 'active_record'
require 'active_record/fixtures'
require 'minitest/autorun'
require 'logger'

# This connection will do for database-independent bug reports.
ActiveRecord::Base.establish_connection(adapter: 'sqlite3', database: ':memory:')
ActiveRecord::Base.logger = Logger.new(STDOUT)

ActiveRecord::Schema.define do
  create_table :students, force: true do |t|
  end

  create_table :classrooms, force: true do |t|
  end

  create_table :enrollments, force: true do |t|
    t.integer :classroom_id
    t.integer :student_id

    t.timestamps null: false
  end
end

class Student < ActiveRecord::Base
  has_many :enrollments
  has_many :classrooms, through: :enrollments
end

class Classroom < ActiveRecord::Base
  has_many :enrollments
  has_many :students, through: :enrollments
end

class Enrollment < ActiveRecord::Base
  belongs_to :student
  belongs_to :classroom
end

class BugTest < Minitest::Test
  def test_hmt_fixture_loading
    # One expects these 2 models to be enough, but including enrollments does not work either
    ActiveRecord::FixtureSet.create_fixtures('./', ['classrooms', 'students'])
    # => ActiveRecord::StatementInvalid: SQLite3::ConstraintException: NOT NULL constraint failed ...
  end
end

classrooms.yml

teachers_class: {}

enrollments.yml

# Attempting to load times explicitly has no effect

one:
  classroom: teachers_class
  student: jonny
  created_at: <%= Time.now %>
  updated_at: <%= Time.now %>

students.yml

jonny:
  classrooms: teachers_class