default or selected kernelversion does not have config value CONFIG_TEST_RUNTIME.
Result is shown for kernelversion 6.6.75

CONFIG_TEST_RUNTIME (not configurable)

configname: CONFIG_TEST_RUNTIME

Linux Kernel Configuration
└─>Kernel hacking
└─>Kernel Testing and Coverage
└─>Runtime Testing
└─>TEST_RUNTIME
In linux kernel since version 6.13 (release Date: 2025-01-19)