Why does setting Maven surefire forkMode to never speed up my unit tests?

Question

With the maven surefire plugin I can set forkMode to never - doing this speeds up execution on 1000 unit tests from 7 minutes to 1:40.

Why is this making such a difference?

Answer 1

I turned on debug for maven and it became clear the pom was referencing a parent pom version which was setting forkMode=always for the surefire plugin, overriding the default value.

Answer 2

The default value of forkMode is once. This means surefire creates a separate JVM to run the tests. Seems on your build system, creating and cleaning up the extra JVM is taking a while.