code: def test_forward_call_with_mixed_case_grapheme_only(self):
      input_text = "Hello world."
      expected_output = [
          self.GRAPHEME_PREFIX + char if char not in " ." else char
          for char in input_text
      ]
      g2p = self._create_g2p(
          use_chars=True,
          phoneme_probability=0.0,
          grapheme_case=GRAPHEME_CASE_MIXED,
          grapheme_prefix=self.GRAPHEME_PREFIX,
      )
  
      phonemes = g2p(input_text)
      assert phonemes == expected_output
  
imports: import os
  import unicodedata
  import pytest
  from nemo.collections.tts.g2p.models.i18n_ipa import IpaG2p
  from nemo.collections.tts.g2p.utils import GRAPHEME_CASE_LOWER, GRAPHEME_CASE_MIXED, GRAPHEME_CASE_UPPER
label_desc: Use image node_id 11 for calling the TestIpaG2p obj's underlying member method code with example usage: obj.test_forward_call_with_mixed_case_grapheme_only() without return types