code: def test_prf_score():
      cand = {"hi", "ho"}
      gold1 = {"yo", "hi"}
      gold2 = set()
  
      a = PRFScore()
      a.score_set(cand=cand, gold=gold1)
      assert (a.precision, a.recall, a.fscore) == approx(
          (0.5, 0.5, 0.5)
      )
  
      b = PRFScore()
      b.score_set(cand=cand, gold=gold2)
      assert (b.precision, b.recall, b.fscore) == approx(
          (0.0, 0.0, 0.0)
      )
  
      c = a + b
      assert (c.precision, c.recall, c.fscore) == approx(
          (0.25, 0.5, 0.33333333)
      )
  
      a += b
      assert (a.precision, a.recall, a.fscore) == approx(
          (c.precision, c.recall, c.fscore)
      )
  
file_path: spacy/spacy/tests/test_scorer.py
imports: import pytest
  from numpy.testing import assert_almost_equal, assert_array_almost_equal
  from pytest import approx
  from spacy.lang.en import English
  from spacy.scorer import PRFScore, ROCAUCScore, Scorer, _roc_auc_score, _roc_curve
  from spacy.tokens import Doc, Span
  from spacy.training import Example
  from spacy.training.iob_utils import offsets_to_biluo_tags
label_desc: Use image node_id 11 for calling a global function with example usage: test_prf_score() without return types