When kgdb is enabled in the kernel config you can also elect to enable the config parameter KGDB_TESTS. Turning this on will enable a special kgdb I/O module which is designed to test the kgdb internal functions.
The kgdb tests are mainly intended for developers to test the kgdb internals as well as a tool for developing a new kgdb architecture specific implementation. These tests are not really for end users of the Linux kernel. The primary source of documentation would be to look in the drivers/misc/kgdbts.c file.
The kgdb test suite can also be configured at compile time to run the core set of tests by setting the kernel config parameter KGDB_TESTS_ON_BOOT. This particular option is aimed at automated regression testing and does not require modifying the kernel boot config arguments. If this is turned on, the kgdb test suite can be disabled by specifying "kgdbts=" as a kernel boot argument.