Originally Posted by
Ian W
This is true, But that doesn't excuse avoiding regression testing. The new use might just have some operational assumptions such as parameters that the designer of the legacy system believed 'would never be exceeded' - and all the people who knew of those parameters and the operational assumptions that drove them are long retired.
But what gets tested in regression testing? Regression testing isn't usually a full formal qualification test, it's a subset of the most important functions. If you get that list wrong, or don't exercise it fully you can miss things.
A full qualification test on one box/software item could take months. That's why they only do regression tests along with testing the new functions.
Say the issue was an assumption that some parameter wouldn't be exceeded. The regression test suite developed isn't going to exceed that either. They are just going to run the same suite as the last time, and the time before that. Only if new functionality is considered important enough will it be added to the regression test. The code could go through a dozen updates without the regression suite being changed.