default or selected kernelversion does not have config value CONFIG_TEST_STRING_HELPERS.
Result is shown for kernelversion 6.9.9

Test functions located in the string_helpers module at runtime

modulename: test-string_helpers.ko

configname: CONFIG_TEST_STRING_HELPERS

Linux Kernel Configuration
└─>Kernel hacking
└─>Kernel Testing and Coverage
└─>Runtime Testing
└─>Test functions located in the string_helpers module at runtime
In linux kernel since version 3.1 (release Date: 2011-10-24)  
source code:
lib/test-string_helpers.c