This is how i am initialising fragment in my unit test. Hope this helps.
import android.support.v4.app.Fragment;
Fragment myFragment = new Fragment();
myActivity = (MyActivity) Robolectric.setupActivity(MyActivity.class);
FragmentManager fm = (FragmentManager) myActivity.getSupportFragmentManager();
String tag = myFragment.class.getSimpleName();
fm.beginTransaction().add(fragment,tag).commit();
fm.executePendingTransactions();
//verify if fragment is visible
String currentState = myFragment.getLifecycle().getCurrentState().toString();
assertEquals("RESUMED", currentState);