Can you accumulate technical dept, even if you regularly clean up your sources meticulously? A short while ago I would have said that this is possible but unlikely. That was before I started taking on the migration of all of OpenFastTrace‘s unit tests from JUnit4 to JUnit5.

Like most non-trivial projects OFT accumulated quite a number of unit tests over the years and although it was always the plan to move to JUnit5 some day, they were all written for JUnit4. With the arrival of OFT 2.0.0 — which also was a major refactoring endeavor — I felt now would be the perfect time to make that migration happen. After all I was in the refactoring flow.

# To rule them all…

Shouldn’t take long, right? Boy was I mistaken. The one thing I completely underestimated was how dependent many of our integration tests were on JUnit rules like Stefan Birkner’s “JUnit System Rules“. While getting the dependencies right in the Maven POM was only slightly harder than anticipated, migrating all parts where rules were used took way longer. I quickly found a replacement for the “Temporary Folder API“: JUnit Pioneer’s “TempDirectory Extension“.

# Homebrew extensions

I did not find a suitable replacement of the JUnit System Rules though, so I decided to take matters into my own hands and create the “JUnit5 System Extensions“. At the time of this writing they cover System.out, System.err and System.exit assertions.

It was a good if also painful practice for writing JUnit5 extensions. Only later I realized that Stefan seems to have started a port of his rules, but it did not look finished to me. Anyway this gave me the opportunity to dive deeper into the JUnit 5 life cycle.

# Run baby, run baby, run baby, run!

Christoph was the one who pointed out to me, that the tests I wrote only ran in Eclipse but were silently skipped when triggered by Maven. The culprit was an older version of the Surefire plugin for Maven. Turns out that you need 2.22.1.

# Simply beautiful

Even though the migration turned out to be much more of a pain than anticipated, especially integration tests and test that check for exceptions looks much nicer thanks to JUnit5. It’s about time for this upgrade, and I am sure we won’t regret this when writing new tests.