fish_test.rb

require 'test_helper'

class FishTest < ActiveSupport::TestCase
  # Replace this with your real tests.
  def test_fish_belongs_to_pond
    pond = Pond.create!
    fish = pond.fishes.create!()
    assert pond.fishes.member?(fish) # works
    fish = Fish.create(:pond => pond)
    assert pond.fishes.reload.member?(fish) # Does not work
  end
end