Automatic testing and Regression tests

For a couple of minutes a day, I've been creating regression tests for one of my background projects - LuaZ80. I started this to identify which instructions were implemented, and which were working properly.

https://github.com/robzed/LuaZ80

Before that I was using a test file to single step the instructions.

Why I didn't make regression tests before because as well as finding which instructions are implemented (at all or properly) they've found a load of edge cases I'd have never found by manual testing.

Well, one reason is the massive effort required to do so ... I guess several times the amount of time to write the original compiling interpreter!

However, without them I have a project which doesn't work properly - based on the number of mistakes and minor errors I've found. And what use is that?

Additionally I have something to check the operation in the future when changes are made - the true meaning of regression tests.