Autoload doesn't work in test [#1312072]

I made a module with .inc file witch contains a class. When I made an object in test case the system didn't find my class. (When I made an object in .module it worked well)

How reproduce this bug:

1. Install a fersh 8.x drupal with minimal profile.
2. put the test module in the sites/all/modules directory.
3. Enable core testing and test module.
4. Run test testcases.
You will see a following:
test pass
5. delete second line (new foo()) in the .module file
You will see the problem:
test failed