tests: Reintroduce ticker test.

This test was removed because of its memory footprint.
Most of the memory consummed by the test itself was related to the instantion of test cases in RAM.

With the introduction of case_t which allows tests cases to live in FLASH, the memory footprint has been drastically reduced (860 bytes of RAM saved) and the ticker test can be reintroduced in the code base.

Author: pan-