The file unittest.hpp provides the gtest framework. Because it's not called out explicitly, The current include order description implicitly suggests it should be in the block of normal HotSpot includes in the usual sorted location. But actual usage mostly places it last of all the includes. There may be technical reasons for preferring that location. The file itself contains a comment saying it's supposed to be last, because of how it handles some annoying macro pollution from some system headers on some platforms. Handling of the HotSpot assert vs standard assert might be another reason, though the handling of that has been improved. There may be other reasons.