What is causing "exception in phase 'instruction selection' " in Groovy / Grails unit test?

Question

Occasionally, when making some updates to a Grails unit test, I will run into an error along the following lines:

BUG! exception in phase 'instruction selection' in source unit ... unexpected NullpointerException

What causes this? Or what is the best strategy to debug this problem?

Plausive

What version of Grails? These BUG! errors should usually be reported to the Groovy team when encountered (assuming you can make a really small test case that exhibits the problem) – Canvass

Answer 1

My best approach thus far has been to iteratively comment things out until the code compiles. A grails clean does not fix the issue.

Using this process I've found that the problem is my @TestFor(Class) annotation. I had moved some code from a service to a class in src/groovy. This appears to have caused the annotation to break. I don't really understand why specifically this breaks, but that was sufficient for me to get things working.

So try removing the @TestFor() annotation if your class under test is not a service or controller or similar.

If that doesn't work, comment everything out and add back one piece at a time.

Plausive

Unbelievable that this is still an issue in 2017. – Winkler

@Winkler I'm think that is a completely unfair comment. For one thing, I haven't encountered this issue since I answered the question. Second, the issue was really a mistake in my code, but the error I received simply didn't point me directly to that. As I mentioned in my answer, the @TestFor() annotation doesn't make sense "if your class under test is not a service or controller or similar." Not a bug in grails or groovy that hasn't been resolved. – Plausive

I encountered the same issue from controller test code generated by Grails - it doesn't compile until you comment out @TestFor(NameOfController.class). – Winkler

Answer 2

In my case my service class don't have default constructor. I resolved this issue by providing default constructer As, @TestFor wants to inject service bean, as my service bean don't have default constructor spring container unable to inject.

Porta