docstr: Test initialization with special characters in the name.
docstr_tok: ["Test","initialization","with","special","characters","in","the","name","."]
code: def test_special_character_name(self):
      """Test initialization with special characters in the name."""
      with self.assertRaisesRegex(ValueError, "Cannot convert"):
          DTypePolicy("@mixed_float16!")
  
imports: from keras.mixed_precision import DTypePolicy
  from keras.mixed_precision import dtype_policy
  from keras.mixed_precision import set_dtype_policy
  from keras.testing import test_case
label_desc: Use image node_id 2 for calling the DTypePolicyEdgeCasesTest obj's underlying member method code with example usage: obj.test_special_character_name() without return types