It's convenient to use a common SetUp for a set of tests. But as data is added to the SetUp, it's good to avoid breaking existing tests. We saw several ways of doing that.
It's straightforward to write tests that set the date and time.
It's useful to make business objects, such as business transactions, explicit in the tables in the tests. For example, user operations as a part of the transaction, such as making payments, are treated as actions in the transaction table in the test.
We showed some examples of sad-path tests, which check when things go wrong.