I had this problem and managed to fix it by manually editing the corresponding * .xcscheme file.
Assuming you have configured the Run configuration for this, you will see the following in the file *.xcscheme:
<LaunchAction
...
debugAsWhichUser = "root"
...>
...
</LaunchAction>
TestAction:
<TestAction
...
debugAsWhichUser = "root"
...>
...
</TestAction>
XCode, , :
, !
* , 8.1 (8B62), , , YMMV.