Use DatabaseCleaner :deletion instead of :truncation in tests for performance
What
Replace use of DatabaseCleaner :truncation
with DatabaseCleaner :deletion
strategy.
Initially I'll just use this to see if tests still pass reliably and measure performance impact.
Why
After checking in log/test.log
I discovered database truncation was taking 500ms to 860ms per test.
A quick search found http://sevenseacat.net/posts/2015/use-database-cleaners-deletion-strategy/ which suggested we use :deletion
instead. An small trial appeared to shave ~500ms off each test, so worth exploring further.
Relevant issues
Closes #30783 (moved)