Add tests for NetTest
Add tests for NetTest

Test loading NetTestCase with required options and verify that
the appropriate exceptions are raised.

0xPoly/ooni-probe,0xPoly/ooni-probe,lordappsec/ooni-probe,Karthikeyan-kkk/ooni-probe,Karthikeyan-kkk/ooni-probe,juga0/ooni-probe,0xPoly/ooni-probe,lordappsec/ooni-probe,lordappsec/ooni-probe,lordappsec/ooni-probe,0xPoly/ooni-probe,juga0/ooni-probe,juga0/ooni-probe,kdmurray91/ooni-probe,juga0/ooni-probe,Karthikeyan-kkk/ooni-probe,kdmurray91/ooni-probe,Karthikeyan-kkk/ooni-probe,kdmurray91/ooni-probe,kdmurray91/ooni-probe