How to mix gflags and gtest

gflags is a C++ library to process command-line flags. A program that uses both Google Test (gtest) and gflags needs to be careful because both of these libraries require to read the input arguments to the program and provide output for --help usage.

What works is to process the input arguments through gtest first and gflags only later:

::testing::InitGoogleTest(&argc, argv);
google::ParseCommandLineFlags(&argc, &argv, true);

The other way around does not work.