When I was working in implements privacy for tool_mobile (MDL-61944) and I was checking an error in a general test, I can see a wrong class path in the return array with a print_object:

print_object(core_component::get_component_classes_in_namespace('tool_mobile', ''));

Result:

  ...

    [tool_mobile\privacy\provider] => Array

        (

            [0] => tool_mobile\

        )

...

When I was expecting this:

  ...

    [tool_mobile\privacy\provider] => Array

        (

            [0] => tool_mobile\privacy

        )

...

You can test it easly in this branch MDL-61944 editing lib/tests/component_test.php and add this print_object inside test_get_component_classes_int_namespace() and then launch:
vendor/bin/phpunit --verbose core_component_testcase lib/tests/component_test.php