The regression test [1] for our legacy application takes five hours to run. It takes five hours to run because it also needs to check every log message (via syslog) to ensure every transaction happened.
I can't say it saves any time, and it certainly does not have a negative cost.
[1] There are no unit tests, as there are no real "units" to test. It's a legacy code base of C and C++, using a proprietary library that no one left in the company has much experience with. Said proprietary library is considered "legacy" by the company that owns it. I've seen the code. No wonder they consider it "legacy" (it started life in the mid-80s and god does it show).
I can't say it saves any time, and it certainly does not have a negative cost.
[1] There are no unit tests, as there are no real "units" to test. It's a legacy code base of C and C++, using a proprietary library that no one left in the company has much experience with. Said proprietary library is considered "legacy" by the company that owns it. I've seen the code. No wonder they consider it "legacy" (it started life in the mid-80s and god does it show).