'Rails test database is not been rollbacked after each tests

I am debugging a rails 5 application. It is supposed to use transactional fixtures.

#test_helper.rb
self.use_transactional_tests = true

But I am tracing the tests and finding that some updates to the database on one test, causing another test to fail because it's not rolling back.

What could be the cause of not rolling back database after each test?

ruby-on-rails

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