ALE Spice Directory Fix (#382)

* Set mission directories to an empty list if ALESPICEROOT is not set

* Removed ALESPICEROOT environment variable not set warning

* Add and update tests for when no ALESPICEROOT is set

ale/__init__.py

@@ -19,7 +19,6 @@ else:
 try:
     spice_root = os.environ['ALESPICEROOT']
 except:
-    warnings.warn('ALESPICEROOT environment variable not set, Spice Drivers will not function correctly')
     spice_root = None
 
 # bring ale stuff into main ale module

tests/pytests/test_env.py

@@ -6,7 +6,6 @@ import ale
 
 def test_env_not_set(monkeypatch):
     monkeypatch.delenv('ALESPICEROOT', raising=False)
-    with pytest.warns(UserWarning, match='ALESPICEROOT environment variable not set'):
     reload(ale)
     assert not ale.spice_root