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Time consuming database entity lookups - In writing API level tests, datasets are still used to get to a known state savings several lines of code. There is a minor drawback with using the datasets however - i.e. having to browse the database to lookup entity ids and such. A straightforward solution to this would be to write a 'cheatsheet' for each dataset perhaps in the Wiki for quick reference.
Example
Take a look at SavingsTest.java in hudsonBuildMifos-4174