Found only one solution for this problem.
When I build my unit-tests, the main bundle’s path is not equal to my project’s bundle (created .app file). Moreover, it’s not equal to LogicTests bundle (created LogicTests.octest file).
Main bundle for unit-tests is something like /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator3.1.3.sdk/Developer/usr/bin. And that’s why program can’t find necessary resources.
And the final solution is to get direct bundles:
NSString *path = [[NSBundle bundleForClass:[myClass class]] pathForResource:name ofType:@"png"];
instead of
NSString *path = [[NSBundle mainBundle] pathForResource:name ofType:@"png"];