Following is a very simple example for describe this issue. ```rb require 'test_helper' describe 'test /stocks' do it 'test /stocks return a stock lists' do exchange = Exchange.create(name: 'nyse') create(:stock, name: 'ge', exchange: exchange, percent_of_institutions: 0.5525, id: 1) create(:stock, name: 'lu', exchange: exchange, percent_of_institutions: 0.2233, id: 2) get "/stocks" last_response.body.must_equal File.read('test/stocks.html') end end ``` will return following error message: ``` ╰─ $ 1 rake test TEST=test/stocks_test.rb RACK_ENV=test DB connected: postgres://postgres:postgres@localhost:5432/marketbet_crawler_test Eager loading ... Run options: --seed 7382 # Running: E Fabulous run in 0.006004s, 166.5512 runs/s, 0.0000 assertions/s. 1) Error: test /stocks#test_0001_test /stocks return a stock lists: Sequel::UniqueConstraintViolation: PG::UniqueViolation: ERROR: duplicate key value violates unique constraint "exchanges_name_key" DETAIL: Key (name)=(nyse) already exists. /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel_pg-1.14.0/lib/sequel/extensions/pg_streaming.rb:113:in `check' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel_pg-1.14.0/lib/sequel/extensions/pg_streaming.rb:113:in `yield_each_row' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel_pg-1.14.0/lib/sequel/extensions/pg_streaming.rb:113:in `block in fetch_rows' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/adapters/postgres.rb:146:in `execute' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/adapters/postgres.rb:500:in `_execute' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel_pg-1.14.0/lib/sequel/extensions/pg_streaming.rb:47:in `_execute' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/adapters/postgres.rb:318:in `block (2 levels) in execute' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/adapters/postgres.rb:522:in `check_database_errors' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/adapters/postgres.rb:318:in `block in execute' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/connection_pool/threaded.rb:88:in `hold' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/database/connecting.rb:269:in `synchronize' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/adapters/postgres.rb:318:in `execute' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/dataset/actions.rb:1093:in `execute' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel_pg-1.14.0/lib/sequel/extensions/pg_streaming.rb:112:in `fetch_rows' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/dataset/actions.rb:946:in `with_sql_each' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/dataset/actions.rb:954:in `with_sql_first' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/adapters/shared/postgres.rb:1721:in `insert_select' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1739:in `_insert_select_raw' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1712:in `_insert' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1784:in `block (2 levels) in _save' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1038:in `around_create' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1781:in `block in _save' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1038:in `around_save' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1776:in `_save' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1488:in `block (2 levels) in save' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1942:in `block in checked_transaction' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/database/transactions.rb:258:in `_transaction' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/database/transactions.rb:233:in `block in transaction' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/connection_pool/threaded.rb:92:in `hold' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/database/connecting.rb:269:in `synchronize' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/database/transactions.rb:195:in `transaction' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1942:in `checked_transaction' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1488:in `block in save' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1930:in `checked_save_failure' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:1488:in `save' /home/zw963/others/.rvm/gems/ruby-3.0.2@marketbet_crawler/gems/sequel-5.49.0/lib/sequel/model/base.rb:254:in `create' /home/zw963/Stocks/marketbet_crawler/test/stocks_test.rb:5:in `block (2 levels) in <top (required)>' ``` ----------------------- Only if change policy to `truncation`, all test passed now.