I'm not too interested in the details of the problem this time, but this is something that keeps coming back, and I feel we're stubborn in not using the /tmp directories like everyone should.
We don't have any benefit from avoiding it right?

There are many limitations of not using tmp:

• can't run multiple testuistes at once
• my /tmp is tuned for temporary, my partitions dedicated to source code I prefer using for reliable stuff
• easy to find on need, and I don't refer to us (anything will be easy for us as we learn) but to the occasional contributor, using /tmp is the least surprising thing
• can't use proven methods - like the JUnit helpers and relatest TestRule

And I see no benefit of insisting to keep it in the source directory?