CTEST_BUILD_CONFIGURATION variable is not documented
According to the doc, the variable exists and used. See CONFIGURATION parameter of ctest_build(): https://cmake.org/cmake/help/latest/command/ctest_build.html?highlight=ctest_build_configuration
But it is not documented in list of variables: https://cmake.org/cmake/help/latest/manual/cmake-variables.7.html?highlight=cmake_major_version