class_docstr: Test shared Alert class.
code: def _customized_alert():
      return Alert(
          "test_rule",
          {"abc": 123},
          {
              "aws-firehose:alerts",
              "aws-sns:test-output",
              "aws-s3:other-output",
          },
          alert_id="abc-123",
          attempts=1,
          cluster="",
          context={"rule": "context"},
          created=datetime.utcnow(),
          dispatched=datetime.utcnow(),
          log_source="source",
          log_type="csv",
          merge_by_keys=["abc"],
          merge_window=timedelta(minutes=5),
          outputs_sent={"aws-sns:test-output"},
          rule_description="A Test Rule",
          source_entity="entity",
          source_service="s3",
          staged=True,
      )
  
imports: import copy
  from datetime import datetime, timedelta
  import json
  from nose.tools import assert_equal, assert_false, assert_is_instance, assert_not_in, assert_raises, assert_true
  from streamalert.shared.alert import Alert, AlertCreationError
label_desc: Use image node_id 2 for calling the TestAlert obj's underlying member method code with example usage: obj._customized_alert() and returns: Alert