android - Can't create directory in internal storage from instrumented test -

i trying create directory instrumented test file.mkdirs() returns false. code i'm using:

file localaroot = instrumentationregistry.getcontext().getdir("locala", context.mode_private); boolean exists = localaroot.exists(); if (!exists) {   exists = localaroot.mkdirs(); } system.out.println("exists = " + exists); ----- exists = false 

how can create directory?