doctest
Fastest feature-rich C++11/14/17/20 single-header testing framework
...The framework is and will stay free but needs your support to sustain its development. There are lots of new features and maintenance to do. There are many C++ testing frameworks - Catch, Boost.Test, UnitTest++, cpputest, googletest and others. The key differences between it and other testing frameworks are that it is light and unintrusive. Ultra light on compile times both in terms of including the header and writing thousands of asserts. Doesn't produce any warnings even on the most aggressive warning levels for MSVC/GCC/Clang.