code: def test_span_squad(self):
      ref = "a string"
      ans_span = "start:2 end:3"
      context = "this is a string! it has the answer."
      self.assertDictClose(
          metrics.span_squad(
              [
                  {"answers": ["", ref], "context": context},
                  {"answers": [ref, ref], "context": context},
              ],
              [ans_span, ans_span],
          ),
          {"em": 100, "f1": 100},
      )
  
imports: from unittest import mock
  from absl.testing import absltest
  import numpy
  import seqio
  import sklearn.metrics
  from t5.evaluation import metrics
  from t5.evaluation import test_utils
label_desc: Use image node_id 10 for calling the MetricsTest obj's underlying member method code with example usage: obj.test_span_squad() without return types