You should see something like this:
<...U-Boot banner...>
- Running 18 driver model tests
+ Running 19 driver model tests
Test: dm_test_autobind
Test: dm_test_autoprobe
Test: dm_test_bus_children
Device 'd-test': seq 3 is in use by 'b-test'
Device 'c-test@0': seq 0 is in use by 'a-test'
Device 'c-test@1': seq 1 is in use by 'd-test'
+ Test: dm_test_bus_children_funcs
Test: dm_test_children
Test: dm_test_fdt
Device 'd-test': seq 3 is in use by 'b-test'