Test helper for changing counts

models_helper.rb

module ModelsHelper
  # Expects that only the passed in models have counts that change. For this we
  # look at all ActiveRecord models, and store their counts.
  #
  # Example: `expect_only_counts_changing(Trip: -1) { Trip.first.delete }`
  #
  # This gives stronger guarantees against future models being affected
  # unexpectedly by other parts of the code base.
  def expect_only_counts_changing(expected_changes)
    previous_counts = ModelsHelper.counts
    yield
    new_counts = ModelsHelper.counts

    changes = new_counts.map do |name, count|
      change = count - previous_counts[name]
      [name, change] unless change.zero?
    end.compact.to_h

    expect(changes).to eq(expected_changes)
  end

  # TODO: update all this with counts that you care about in your application.
  EXCLUDED_CLASSES = [PaperTrail::Version, PaperTrail::VersionAssociation].freeze
  def self.counts
    Rails.application.eager_load!
    models = ActiveRecord::Base.descendants - EXCLUDED_CLASSES
    models.map { |model| [model.name.to_sym, model.count] }.to_h
  end
end

RSpec.configure do |config|
  config.include ModelsHelper
end