Without regard to the code itself, I'd break the test into parts. First I'd test that I get a response from the object instantiation. Then, I'd test to see if it showed the network device attached. Based on the result of the previous test, I'd test communicating with the device or skip this test.

It sounds, though, like your code doesn't have this kind of granularity for the test suite to test. Perhaps you should consider creating the object either way, as you already suggested. You could then have a status method for it which reports presence or absence of the device. Further future tests could be skipped if the device is not determined to be present.