I'd rather have an existing suite of tests that I can use to verify that when working with other people's code.
And more importantly, if JIRAISSUE-15295 is reproducible, then a unit test that a) reproduces it and b) verifies that the bug no longer occurs, is invaluable to prevent someone bringing JIRAISSUE-15295 back from the dead.
Of course, if the unit test is too tightly coupled, and has too many insights into code it shouldn't, then it's worthless as JIRAISSUE-15295 will most likely reoccur via a different code path.
But, poorly written unit tests aside, I have found significant value in unit tests when maintaining a rapidly changing code base.
A rapidly changing codebase is where unit tests are least useful though. Most of the changes are going to be because of new requirements which just means the test has to be updated. It's just busywork at that point.
If you have discovered a way to write unit tests that can tell the difference between a regression and an enhancement, please let me know.
And more importantly, if JIRAISSUE-15295 is reproducible, then a unit test that a) reproduces it and b) verifies that the bug no longer occurs, is invaluable to prevent someone bringing JIRAISSUE-15295 back from the dead.
Of course, if the unit test is too tightly coupled, and has too many insights into code it shouldn't, then it's worthless as JIRAISSUE-15295 will most likely reoccur via a different code path.
But, poorly written unit tests aside, I have found significant value in unit tests when maintaining a rapidly changing code base.