Prioritizing error case testing
For all the test cases described in this chapter, remember that the more obscure your failure mode, the lower priority the bug will be. Testing error cases is always less important than tests that cover the main functionality of a new feature since if they fail, that feature won’t work at all. Error cases shouldn’t usually happen, so their rarity lessens their impact. The more obscure the failure case, the rarer it is and is even less critical. Error case testing should be tempered with a knowledge of that priority. You can run this area of testing last, for instance, alongside the maintainability tests, which don’t affect customers directly, and destructive tests, which are another failure mode.
On the other hand, it is difficult to know in advance how bad any failures will be. For instance, if there is a bug when adding too many users, you will probably receive an unhelpful error message. That is a bug, but not a high-priority...
