class_docstr: Tests for BigQuery Read.
class_docstr_tok: ["Tests","for","BigQuery","Read","."]
code: def test_create_reader_dataset_not_found(self):
      parallelism = 4
      bq_ds = BigQueryDatasource(
          project_id=_TEST_GCP_PROJECT_ID,
          dataset="nonexistentdataset.mocktable",
      )
      with pytest.raises(ValueError) as exception:
          bq_ds.get_read_tasks(parallelism)
      expected_message = "Dataset nonexistentdataset is not found. Please ensure that it exists."
      assert str(exception.value) == expected_message
  
imports: from unittest import mock
  import pyarrow
  import pytest
  from google.api_core import exceptions, operation
  from google.cloud import bigquery, bigquery_storage
  from google.cloud.bigquery import job
  from google.cloud.bigquery_storage_v1.types import stream
  import ray
  from ray.data.datasource import BigQueryDatasource, _BigQueryDatasink
  from ray.data.tests.conftest import *
  from ray.data.tests.mock_http_server import *
  from ray.tests.conftest import *
label_desc: Use image node_id 5 for calling the TestReadBigQuery obj's underlying member method code with example usage: obj.test_create_reader_dataset_not_found() without return types