code: def test_add_metric_to_cache_fail_unit(self):
      metrics_cache_obj = MetricsCacheYamlImpl(
          os.path.join(dir_path, "metrics.yaml")
      )
      with pytest.raises(merrors.MetricsCacheTypeError) as exc_info:
          metrics_cache_obj.add_metric_to_cache(
              metric_name="test_add_metric_to_cache_fail_unit",
              unit=["foo"],
              dimension_names=["ModelName", "Host"],
              metric_type=MetricTypes.GAUGE,
          )
      assert str(exc_info.value) == "`unit` must be a str"
  
imports: import os
  import uuid
  import pytest
  import ts.metrics.metric_cache_errors
  from ts.metrics.caching_metric import CachingMetric
  from ts.metrics.dimension import Dimension
  from ts.metrics.metric_cache_yaml_impl import MetricsCacheYamlImpl
  from ts.metrics.metric_type_enum import MetricTypes
label_desc: Use image node_id 5 for calling the TestAddMetrics obj's underlying member method code with example usage: obj.test_add_metric_to_cache_fail_unit() without return types