Add some model tests (#9)

Reviewed-on: #9

test/system/expenses_test.rb

@@ -2,7 +2,7 @@ require "application_system_test_case"
 
 class ExpensesTest < ApplicationSystemTestCase
   setup do
-    @expense = expenses(:one)
+    @expense = expenses(:monthly_expense)
   end
 
   test "visiting the index" do

test/system/incomes_test.rb

@@ -2,7 +2,7 @@ require "application_system_test_case"
 
 class IncomesTest < ApplicationSystemTestCase
   setup do
-    @income = incomes(:one)
+    @income = incomes(:included_1)
   end
 
   test "visiting the index" do