Rails Test to Confirm Column Updated - ruby-on-rails

Question

I am using Minitest and have a controller like this:
def update
authorize #flag
respond_to do |format|
if #flag.update(flag_params)
format.html { redirect_to flags_path , success: "#{#flag.name} was successfully updated." }
format.js
else
format.html { render :edit }
# format.js
end
end
end
I have a JS remote select that triggers a form submit and then returns a DataTable update. Works fine in development etc. I commented out the format for the else to force a no format error if the update fails.
Here is my test:
test "should assign flag" do
assert_changes 'flags(:one).assigned_id' do
patch flag_url flags(:one), format: :js, params: { flag: { assigned_id: users(:operator).id } }
end
end
The asssigned_id is nil for flags(:one) and all the patch does it update that column to the id from a user fixture. Yet my test fails:
FAIL FlagsControllerTest#test_should_assign_flag (44.56s)
"flags(:one).assigned_id" didn't change
test/controllers/flags_controller_test.rb:38:in `block in <class:FlagsControllerTest>'
Yet this passes:
patch flag_url #flag, format: :js, params: { flag: { assigned_id: users(:operator).id } }
assert_response :success
Also this fails:
assert flags(:one).assigned_id_changed?
I have double checked my tests / code and don't think I am missing anything here.
Have I missed something obvious or perhaps I am not applying the assertions correctly?
UPDATED INFO FOR ANSWER
Here is my updated model test:
require 'test_helper'
class FlagTest < ActiveSupport::TestCase
fixtures :flags
let(:flag_one) { flags(:one) }
end
and controller test:
require 'test_helper'
class FlagsControllerTest < ActionDispatch::IntegrationTest
test "should assign flag" do
assert_changes 'flag_one.assigned_id' do
patch flag_url flag_one, format: :js, params: { flag: { assigned_id: users(:operator).id } }
end
end

Answer 1

Think the issue is that when you call the fixture directly in code like so...
assert_changes 'flags(:one).assigned_id' do
patch flag_url flags(:one), format: :js, params: { flag: { assigned_id: users(:operator).id } }
end
..the test reloads the instance from the fixture and of course it is unchanged. I've never written a test with a fixture reference inline. What I usually do is set up a let using the value from the fixture...
class FlagTest < ActiveSupport::TestCase
fixtures :flags
let(:a_flag){flags(:one)}
and then use that in my tests.
test "should assign flag" do
assert_changes 'a_flag.assigned_id' do
patch flag_url a_flag, format: :js, params: { flag: { assigned_id: users(:operator).id } }
end
end
Saves some typing if you have a number of tests, and should fix your issue.