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

Test IIO formatting functions

modulename: iio-test-format.ko

configname: CONFIG_IIO_TEST_FORMAT

Linux Kernel Configuration
└─>Device Drivers
└─>Industrial I/O support
└─>Test IIO formatting functions
In linux kernel since version 5.2 (release Date: 2019-07-07)  
source code:
drivers/iio/test/iio-test-format.c