Rails - Mar 2006 - unit_tests and deleting from the database

I get errors when running rake test_units:

test_destroy(LocationTest):
ActiveRecord::StatementInvalid: Mysql::Error: #23000Cannot delete or 
update a pa
rent row: a foreign key constraint fails (`overblijf_tst/groups`, 
CONSTRAINT `fk
_groups_locations` FOREIGN KEY (`location_id`) REFERENCES `locations` 
(`id`)): D
ELETE FROM locations

Any pointers??

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