DRY means “don’t repeat yourself”. A lack of repetition is a primary signifier of good, maintainable code.
A good way of cleaning up code is to look for repetitive patterns and de-duplicate them.
Since tests are also code, the same rules apply. Test code should be non-repetitive and tests themselves should be non-repetitive. Tests should regularly be refactored by looking for repetition and removing it by parameterizing your test cases.
Hitch provides the use of Jinja2 as a templating language to let you generate lots of similar tests
without writing a lot of duplicated test cases. See
howto/parameterize_test_cases for a guide
on how to use it.
See also: Don’t Repeat Yourself Wikipedia Page