class_docstr: Test shared EphemeralDriver
code: def __init__(self):
      self._driver = None
  
imports: from nose.tools import assert_equal, assert_raises, assert_true
  from streamalert.shared.lookup_tables.drivers import EphemeralDriver, NullDriver
  from streamalert.shared.lookup_tables.drivers_factory import construct_persistence_driver
  from streamalert.shared.lookup_tables.errors import LookupTablesConfigurationError
label_desc: Use image node_id 1 to create a new TestEphemeralDriver object  with example: obj = TestEphemeralDriver()