class_docstr: Test ArtifactExtractor class 
class_docstr_tok: ["Test","ArtifactExtractor","class"]
docstr: Teardown after each method
docstr_tok: ["Teardown","after","each","method"]
code: def teardown(self):
      """Teardown after each method"""
      ArtifactExtractor._firehose_client = None
  
file_path: streamalert/tests/unit/streamalert/shared/test_artifact_extractor.py
imports: from mock import call, patch
  from nose.tools import assert_equal
  from streamalert.shared.artifact_extractor import Artifact, ArtifactExtractor
  from streamalert.shared.firehose import FirehoseClient
  from tests.unit.streamalert.shared.test_utils import generate_artifacts, generate_categorized_records, MOCK_RECORD_ID
label_desc: Use image node_id 2 for calling the TestArtifactExtractor obj's underlying member method code with example usage: obj.teardown() without return types