Account::Sync model and test fixture simplifications (#968)

* Add sync model

* Fresh fixtures for sync tests

* Sync tests overhaul

* Fix entry tests

* Complete remaining model test updates

* Update system tests

* Update demo data task

* Add system tests back to PR checks

* More simplifications, add empty family to fixtures for easier testing

test/controllers/categories_controller_test.rb

@@ -3,6 +3,7 @@ require "test_helper"
 class CategoriesControllerTest < ActionDispatch::IntegrationTest
   setup do
     sign_in users(:family_admin)
+    @transaction = account_transactions :one
   end
 
   test "index" do
@@ -37,7 +38,7 @@ class CategoriesControllerTest < ActionDispatch::IntegrationTest
 
     assert_difference "Category.count", +1 do
       post categories_url, params: {
-        transaction_id: account_transactions(:checking_one).id,
+        transaction_id: @transaction.id,
         category: {
           name: "New Category",
           color: color } }
@@ -48,7 +49,7 @@ class CategoriesControllerTest < ActionDispatch::IntegrationTest
     assert_redirected_to transactions_url
     assert_equal "New Category", new_category.name
     assert_equal color, new_category.color
-    assert_equal account_transactions(:checking_one).reload.category, new_category
+    assert_equal @transaction.reload.category, new_category
   end
 
   test "edit" do