Cleaning the Database with Truncation
Truncating the database before each scenario is a brute-force technique, and the main drawback is that it’s generally slower than rolling back a transaction. This is why the transactional approach is generally preferable if you can get away with it. The advantage of truncation is that it’s a cleaning strategy that works reliably when we have more than one database connection, since no transactions are used. Let’s modify our cleaning strategy and see how it compares. This is a simple change in our database.rb file, shown below.
Truncating the database in an After hook usually works just as well as doing it in a Before hook, but there is a subtle difference.
First, if the process gets killed before it has time to clean up in the After hook, it might cause the next test run to fail.
Second, when a scenario fails it might not be evident why it failed, and having the ability to peek inside the database as a post-mortem often helps us understand why a scenario is failing.
As you will also see in Isolating Scenarios, this post-mortem technique can be used in other situations as well.
| | require 'database_cleaner' |
| | |
| | DatabaseCleaner.strategy = :truncation |
| | |
| | Before do |
| | DatabaseCleaner.clean |
| | end |
Notice how we removed the After hook and made the Before hook call DatabaseCleaner.clean instead. In truncation mode, DatabaseCleaner.start does nothing, and DatabaseCleaner.clean truncates all tables. In other words, it deletes all rows.
Running Cucumber again makes the scenario pass again:
| | == 1 CreateAccounts: migrating ================================================ |
| | -- create_table(:accounts) |
| | -> 0.0010s |
| | == 1 CreateAccounts: migrated (0.0010s) ======================================= |
| | |
| | Starting transaction_processor in ~/message_queues/01 with |
| | 'ruby lib/transaction_processor.rb' |
| | transaction processor ready |
| | Server transaction_processor (94557) is up. |
| | Feature: Cash Withdrawal |
| | |
| | Scenario: Successful withdrawal from an account in credit |
| | Given my account has been credited with $100 |
| | When I withdraw $20 |
| | Then $20 should be dispensed |
| | And the balance of my account should be $80 |
| | |
| | 1 scenario (1 passed) |
| | 4 steps (4 passed) |
| | 0m2.076s |
| | Shutting down transaction_processor (94557) |
| | Server transaction_processor (94557) is shut down |
That brings us to the end of the worked example. In the next part are a series of recipes for using Cucumber in the wild. Good luck out there!