Unit test execution speed (how many tests per second?)

Question

What kind of execution rate do you aim for with your unit tests (# test per second)? How long is too long for an individual unit test?

I\'d be interested in knowing if

Answer 1

I tend to focus more on readability of my tests than speed. However, I still try to make them reasonably fast. I think if they run on the order of milliseconds, you are fine. If they run a second or more per test... then you might be doing something that should be optimized.

Slow tests only become a problem as the system matures and causes the build to take hours, at which point you are more likely running into an issue of a lot of kind of slow tests rather than one or 2 tests that you can optimize easily... thus you should probably pay attention RIGHT AWAY if you see lots of tests running hundreds of milliseconds each (or worse, seconds each), rather than wait till it gets to the hundreds of tests taking that long point (at which point it is going to be really hard to solve the problem).

Even so, it will only reduce the time between when your automated build issues errors... which is ok if it is an hour later (or even a few hours later), I think. The problem is running them before you check in, but this can be avoided by selecting a small subset of tests to run that are related to what you are working on. Just make sure to fix the build if you check in code that breaks tests you didn't run!